Polyhedron Vol[ 06\ No[ 11\ pp[ 2770Ð2777\ 0887Þ 0887 Elsevier Science Ltd\ Pergamon All rights reserved[ Printed in Great Britain9166Ð4276:87 ,08[99¦9[99PII] S9166Ð4276"87#99036Ð7

Some reaction chemistry oftrans!ðFe"H#"h1!H1#"h

1!dppm#1ŁðBF3Ł[The crystal and molecular structure oftrans!ðFe"H#"CH2CN#"h1!dppm#1ŁðBF3Ł\dppm�bis"diphenylphosphino#methane

Yuan Gao\a David G[ Holah\a� Alan N[ Hughes\a Greg J[ Spivak\a

Matthew D[ Havighurstb and Vincent R[ Magnusonb

aDepartment of Chemistry\ Lakehead University\ Thunder Bay\ Ontario\ Canada\ P6B 4E0[

bDepartment of Chemistry\ University of Minnesota!Duluth\ Duluth\ Minnesota 44701\ U[S[A[

"Received 10 October 0886^ accepted 7 April 0887#

Abstract*Substitution of H1 by ligands "L# in either pure trans!ðFe"H#"h1!H1#"h1!dppm#1Ł ðBF3Ł\ 0\ or solutionsof ðFe"H#1"dppm#1Ł 1\ L and HBF3[Et1O in which 0 is made in situ\ produce the compounds trans!ðFe"H#"L#"h1!dppm#1Ł ðBF3Ł "L1CH2CN\ 2^ succinonitrile\ 3^ pyridine\ 4^ C1H3\ 5^ and N1\ 6#[ The order of H1 replacementfrom 0 appears to be CH2CN×N1×C1H3½pyridine[ Evidence is presented for the protonation of the hydrideligands of 0 or 1 to produce ðFe"H1#1"h1!dppm#1Ł ðBF3Ł1\ 7\ although 7 could not be fully characterized norcould it be obtained in the solid state[ Trans!ðFe"CH2CN#1"h1!dppm#1Ł ðBF3Ł1\ 8\ was obtained from solutionsof 7 treated with acetonitrile[ The coordination geometries of 2\ 8 and 3 "monodentate succinonitrile# havebeen con_rmed by X!ray crystallography "only the gross structural features of 3 were obtained due to a poordata set from a very small crystal#[ Þ 0887 Elsevier Science Ltd[ All rights reserved[

Keywords] bis"diphenylphosphino#methane^ dihydrogen complexes^ dihydrogen displacement reactions^ ironcomplexes^ metal hydride complexes^ X!ray structures[

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There is a body of literature ð0Ð1Ł on metal!dihydrogencomplexes in general and on cations containing FeII\hydride\ dihydrogen and chelating phosphines of thetype trans!ðFe"H#"H1#"P!P#1Ł¦ in particular[ Most ofthese complexes have been well characterized andextensively studied by NMR methods and\ to a lesserextent\ by crystallography[ These compounds havealso been studied from the point of view of intra!molecular exchange of H atoms between H! and H1

ð0Ð1Ł\ the elimination and ligand substitution of H1

ð0Ð1Ł\ and homolytic and heterolytic splitting of dihy!drogen ð1Ł[ Relative to some bis!phosphines\ dppmhas been used less frequently in reactions which pro!

� Author to whom correspondence should be addressed[

2770

duce such complexes although 0 and 1 were brie~yreported\ but not fully characterized\ as being pro!duced from reactions of FeII with dppm and NaBH3

ð2Ł[ In our work on the single!step syntheses of reducedmetal!phosphine complexes\ we also observed ð3Ł thatFeIII! and FeII!dppm mixtures are not reduced beyondFeII by NaBH3 in contrast to the behaviour of high!valent Co\ Ni\ Pd and Pt systems[ Even using LiAlH3

as the reducing agent\ the main product is the FeII

species 1 from which 0 is derived by protonation[These were both isolated and characterized\ 1 by crys!tallography ð3Ł[ This paper describes the substitutionreactions of 0\ reactions involving the protonation of0 and 1 and the molecular structures of threecompounds[

Y[ Gao et al[2771

EXPERIMENTAL

Rea`ents and Solvents

Dppm\ anhydrous FeCl2\ HBF3 = Et1O\ LiAlH3 andLiAlD3 were obtained from Aldrich[ The last threereagents were stored under nitrogen[ When necessaryFeCl2 was dried by heating the hydrated salt underre~ux with SOCl1 ð4Ł[ Compounds 0\ 1 and 2 wereprepared by literature methods ð3Ł[ Benzene and THFwere both dried before use by distilling from Na wire[All solvents were degassed prior to use by purgingwith nitrogen[

Physical Measurements

Both samples and reagents were handled under aninert atmosphere during weighing and data collection[Microanalyses for C\ H and N were acquired in ourlaboratories using a Control Equipment Corporationmodel 139XA analyzer with V1O4 used as a com!bustion aid[ Infrared spectra "for Nujol mulls betweenNaCl plates# were recorded on a Bruker IFS 55 FTIRspectrophotometer[ 0H and 20P"0H# NMR spectrawere recorded on a Bruker AC!E 199 spectrometer[Chemical shifts are reported as d values with positiveshifts for 0H down_eld of the signal of Me3Si "TMS#while those for 20P are down_eld of the signal of exter!nal 74) H2PO3[

Syntheses of the compounds

All the syntheses were performed in a glove boxunder dry "P1O4# nitrogen\ argon\ ethylene or hydro!gen[

Preparation of trans!ðFe"H#"CH2CN#"h1!dppm#1Ł ðBF3Ł"2#

As an alternative to the published procedure ð3Łfor the preparation of 2\ 1 "9[10 g\ 9[15 mmol# wassuspended in CH2CN "09 cm2# and stirred at !29>C"dry ice and acetone# for 19 min[ HBF3 = Et1O "199 ml\0[25 mmol# was added dropwise to the stirred solutionto form an orange red solution[ Ether "49 cm2# wasadded to precipitate the orange yellow solid\ whichwas collected by _ltration\ dried under reduced pres!sure\ and recrystallized from CH1Cl1:hexane[ Yield]75)[ The spectroscopic characteristics "20P and 0HNMR^ FTIR# of this product were identical to thosepreviously published ð3Ł[

Preparation of trans!ðFe"H#"NC"CH1#1CN#"h1!dppm#1Ł ðBF3Ł "3#

"a# A solution of succinonitrile "9[09 g\ 0[14 mmol#in THF "3 cm2# was added to a stirred suspension of0 "9[02 g\ 9[03 mmol# in THF "09 cm2#\ and an orange

red solution was formed immediately[ After 39 min\ether "29 cm2# was added and the resulting orangesolid _ltered o}\ washed twice with ether "09 cm2 eachtime# and dried under reduced pressure[ Yield] 79)[Recrystallization from CH1Cl1:hexane produced thinplates for an X!ray structural determination[ Found]C\ 54[6^ H\ 4[1^ N\ 1[5[ Calc[ for FeF3P3BN1C43H38]C\ 54[3^ H\ 3[8^ N\ 1[7)[ IR] n"Fe!H# 0770 "w#\ n"CN#1117 "vw#\ 1128 "w\b# cm!0[ 20P"0H# NMR "14>C\CD1Cl1#] d 29[2 "singlet#[ 0H NMR "14>C\ CD1Cl1#]d !02[0 "Fe!H\ quintet\ 1JPH � 36 Hz#^ d 3[23 and 3[70"PCHaHbP\ poorly resolved#^ d 1[11\ 0[82 "Fe!NCCH1

CH1CN\ broad signals\ overlapped and poorlyresolved#[ Complex 3 is stable in air[ It is soluble andstable in dichloromethane and chloroform[

"b# Alternatively\ succinonitrile "9[944 g\9[58 mmol# dissolved in THF "3 cm2#\ was added to astirred suspension of compound 1 "9[07 g\ 9[11 mmol#in THF "09 cm2#[ HBF3 = Et1O "199 mL\ 0[25 mmol#was added dropwise[ The clear yellow solution gradu!ally became orange!red[ After 19 min\ ether "29 cm2#was added and the resulting orange solid was _lteredo}\ washed twice with ether "09 cm2 each time# anddried under reduced pressure[ Yield] 70)[

Preparation of trans!ðFe"H#"pyridine#"h1!dppm#1Ł ðBF3Ł"4#

Pyridine "9[0 mL\ 0[13 mmol# was added to a stirredsuspension of 1 "9[00 g\ 9[01 mmol# in THF "09 cm2#to produce a clear red solution[ Addition of ether"29 cm2# precipitated a blood!red solid which waswashed twice with ether "09 cm2 each time# and driedunder reduced pressure[ Yield] 55)[ Since the solidsmells strongly of pyridine\ chemical analyses wereunsatisfactory[ Found] C\ 51[4^ H\ 4[3^ N\ 1[9[ Calc[for FeF3P3BNC44H34] C\ 56[9^ H\ 3[5^ N\ 0[3)[ IR]n"Fe!H# 0742 "w# cm!0[ 20P"0H# NMR "14>C\ deut!erated pyridine#] d 11[56 "singlet#[ 0H NMR "14>C\deuterated pyridine#] d !06 "Fe!H\ quintet\1JPH�35 Hz#[ In solution\ 4 only has limited stabilityin pyridine[ In acetone or methylene chloride it decom!poses quickly and recrystallization attempts wereunsuccessful[

Preparation of trans!ðFe"H#"h1!CH11CH1#"h1!dppm#1ŁðBF3Ł = 9[4CH1Cl1"5#

"a# Ethylene was passed into a stirred suspensionof 0 "9[980 g\ 9[09 mmol# in THF "19 cm2# at a rate of2 bubbles:s for three h[ Addition of ether "19 cm2#precipitated an orange red product which was _lteredo}\ washed with ether "09 cm2# and dried underreduced pressure[ Yield] 78)[ The complex wasrecrystallized from CH1Cl1:hexane under Ar[ Found]C\ 53[4^ H\ 4[04[ Calc[ for FeC41[4H49P3BF3Cl] C\ 53[1^H 4[0)[ IR] n"Fe!H# 0603 "w\ sh# cm!0[ 20P"0H# NMR"14>C\ CDCl2#] d 21[7 "singlet#[ 0H NMR "14>C\CDCl2#] d !0[67 "Fe!H\ quintet\ 1JPH�49[5 Hz#^ d 4[18

Some reaction chemistry of trans!ðFe"H#"h1!H1#"h1!dppm#1Ł ðBF3Ł[ 2772

and 3[28 "PCHaHbP\ poorly resolved#^ d 2[07 "Fe!"h1!CH11CH1##[ Complex 5 is very sensitive to moisture[It is stable in dry acetone\ chloroform and methylenechloride[

"b# Alternatively\ HBF3 = Et1O "099 mL\ 9[57 mmol#was added dropwise to 1 "9[00 g\ 9[026 mmol# in THF"09 cm2# into which ethylene was passed at a rate of2 bubbles:s for three h[ Addition of ether "19 cm2#completed the precipitation of an orange!red solidwhich was _ltered o}\ washed and dried as above[Yield] 61)[

Preparation of trans!ðFe"H#"N1#"h1!dppm#1Ł ðBF3Ł "6#

"a# N1 was passed at a rate of 2!4 bubbles:s for 4 hinto a suspension of 0 "9[01 g\ 9[02 mmol# in THF"19 cm2#[ Addition of ether "19 cm2# produced a yellowsolid which was _ltered o}\ washed twice with ether"09 cm2 each time# and dried under reduced pressure[Yield] 66)[ Recrystallization was carried out fromCH1Cl1 under dry N1[ Found] C\ 53[9^ H\ 3[88^ N\1[41[ Calc[ for FeF3P3BN1C49H34] C\ 52[8^ H\ 3[7^ N\2[9)[ IR] n"Fe!H# 0602 "vw# cm−0\ n"NN# 1005 cm−0[20P"0H# NMR "14>C\ CD1Cl1#] d 13[1 "singlet#[ 0HNMR "14>C\ CD1Cl1#] d !8[27 "Fe!H\ quintet\1JPH�32[5 Hz#[ Complex 6 gradually changes its col!our in air[ In solution 6 is only stable in dry CH1Cl1[It decomposes very quickly in acetone or chloroform[

"b# HBF3 = Et1O "099 mL\ 9[57 mmol# was addeddropwise to a freshly prepared stirred suspension of 1

"9[00 g\ 9[02 mmol# in THF "09 cm2#[ N1 was passedinto the suspension for 4 h[ 6 was isolated as describedabove for 5 "method b#[ Yield] ×59)[

Preparation of trans!ðFe"h1!H1#1"h1!dppm#1Ł ðBF3Ł1 "7#

"a# HBF3 = Et1O "04 mL\ 9[0 mmol# was added drop!wise with shaking to 0 "09 mg\ 9[90 mmol# in CD1Cl1"9[5 cm2# under Ar or N1 to give a clear yellow solu!tion[ 20P"0H# NMR "14>C\ CD1Cl1#] d 2[21 "singlet#[Addition of Et1O produced only pure solid 0\ theidentity of which was con_rmed by 0H and 20P NMRand by IR spectroscopic examination[ A similarexperiment in THF under H1 produced a solution withthe same NMR spectrum "d 2[21#[ Addition of Et1Osaturated with H1 also produced only pure 0[

"b# HBF3 = Et1O "049 mL\ 0 mmol# was added drop!wise to a stirred suspension of 1 "9[00 g\ 9[02 mmol# inTHF "09 cm2# to give a clear yellow solution[ 20P"0H#NMR "14>C#] d 2[21 "singlet#[ Addition of Et1O pro!duced 0 as above[

In spite of repeated attempts under a variety of con!ditions\ no 0H NMR signals up_eld of TMS wereobserved for any solutions thought to contain 7[

Preparation of trans!ðFe"CH2CN#1"h1!dppm#1ŁðBF3Ł1 = 1CH1Cl1 "8#

To a stirred suspension of 1 "9[08 g\ 9[11 mmol# inCH2CN "5 cm2#\ HBF3 = Et1O "049 mL\ 0 mmol# was

added to produce a clear deep!red solution[ Ether"69 cm2# was added immediately and the resultingpeach!colored solid "9[10 g# was _ltered o}\ washedwith ether "09 cm2# and dried under reduced pressure[20P"0H# NMR "14>C\ CD1Cl1#^ d 18[7 "singlet#^ d 03"singlet#^ d 01[2 "triplet# and d 0[97 "triplet# "see dis!cussion#[ The mixture of products "9[10 g# was redis!solved in CH2CN "7 cm2# and stirred overnight[ Ether"69 cm2# was then added to precipitate out a pink solid"9[03 g# which was collected and dried as describedabove[ CH1Cl1 "or CH2CN# "3 cm2# was added to dis!solve the solid and hexane "or ether# "05 cm2# wascarefully layered over the _ltrate[ The _nal crystallineproduct 8\ suitable for the X!ray structure deter!mination\ was deposited within 13 h[ The crystals were_ltered o}\ washed with ether "09 cm2# and dried underreduced pressure[ Yield] 20)[ Found] C\ 43[0^ H\ 3\5^N 1[3[ Calc[ for C45H43P3N1Cl3B1F7Fe] C\ 42[7^ H\3[3^ N\ 1[1)[ IR] n"CN# 1138\ 1158\ 1178\ 1206 cm−0[20P"0H# NMR "14>C\ CD1Cl1#] d 03[1 "singlet#[ 0HNMR "14>C\ CD1Cl1#] d 1[26 ðFe!"NCCH2#1Ł[ Com!plex 8 is stable in air and is soluble and stable inmethylene chloride\ chloroform and acetonitrile[

The reactivity of 0 toward propene\ cis!1!butene andstyrene

When propene or cis!1!butene was used instead ofethylene as outlined above for the synthesis of 5 byprocedure "a#\ or when styrene "0[51 cm2\ 03 mmol#was stirred with 0 "9[02 g\ 9[03 mmol# in THF "09 cm2#\under Ar for 2 h\ no evidence that 0 had reacted wasdetected from NMR measurements[

X!Ray Crystallo`raphy

Crystallographic data collection for 2 and 8 wascarried out on an Enraf!Nonius CAD!3 di}ract!ometer using MoKa graphite!monochromatized radi!ation[ Crystal structure re_nement calculations werecarried out on a PC Express computer with theSHELX program system ð5Ł[ NRCVAX computerprograms were used for scaling and data reductionð6Ł[

For 2\ an absorption correction was applied[ Theattenuation coe.cient used was 0[9 and the averageabsorption correction factor was 9[7036[ The Fe atomwas located by direct methods and all remainingatoms were found by cycles of Fourier and di}erenceFourier calculations[ Calculated ideal positions of theH atoms on the phenyl and methylene C atoms ofdppm and on the methyl C of acetonitrile wereincluded but not re_ned[ The hydride ligand waslocated in the Fourier map and re_ned along withother atoms[ The BF3

− is disordered\ with threerotationally related locations of its four ~uorineatoms[ All atoms\ except H and F\ were re_ned withanisotropic thermal displacement parameters[ Thefour F atoms of each position were re_ned with equal

Y[ Gao et al[2773

B!F distances and equal isotropic thermal dis!placement parameters[

Crystal data for 8] monoclinic\ C1:c\ a�11[4907"4#\b�01[2511"1#\ c�10[5791"4# A� \ b�095[936"0#>\Z�3[ The Fe is on a 1!fold axis so that the asymmetricunit contains the Fe\ one dppm\ one disordered BF3

over two independent positions in a 9[68]9[10 ratio\and one CH1Cl1 which shows signi_cant thermalmotion and therefore contributes to the high residuals[R indices\ as de_ned in ref ð3Ł "all data#] R0�9[0190\wR1�9[1076#[ Relevant bond lengths and angles are]Fe!P"0#�1[1604"03#\ Fe!P"1#�1[1730"02#\ Fe!N�0[898"3#\ N!C�0[0226"6#\ C!C inCH2CN�0[355"7# A� ^ P"0#!Fe!P"1#�62[9> and theinternal P!C!P angle in dppm�83[5>[ These structuralparameters are very similar to those reported ð7Ł fortrans!ðFe"CH2CN#1"dppm#1Ł ðFeI3Ł[1H1O and the pub!lished bond lengths for the latter will be used forcomparison purposes in this paper[

Crystals of 3 were exceptionally thin and conse!quently a poor data set allowed only con_rmation ofthe overall structural features of 3\ namely that thesuccinonitrile is indeed trans to the H! and is coor!dinated to the Fe through one of the nitrile groups ð8Ł[

Supplementary X!ray materials for 2\ includingatomic coordinates and thermal parameters\ havebeen deposited with the Cambridge CrystallographicData Center[

RESULTS AND DISCUSSION

The synthesis of derivatives of 0 can be carried outeither by the direct replacement of the dihydrogenligand in pure 0 by several small ligands or from 0

prepared in situ by protonating 1 in the presence ofthe ligands[ Care must be taken to ensure anhydrousconditions for reproducibility of the reactions[ Theligands selected "CH2CN\ succinonitrile\ pyridine\C1H3\ CO ð3Ł and N1# have widely varying s donor!pacceptor properties and can bind to the Fe center inan end on or side on fashion[ The fact that ethylene\but not propene\ cis!1!butene or styrene\ can replace

Scheme 0[

the H1 indicates that the site is sterically constrained[Pyridine replaces the H1 and although the resultingcomplex is quite unstable\ the complex shows a strongsinglet in the 20P NMR spectrum and the expectedhydride quintet in the 0H NMR spectrum[ Both pyri!dine and ethylene are\ in turn\ displaced from theirrespective complexes by N1[ Acetonitrile is ideallysuited to the site and rapidly replaces\ not only H1\but pyridine\ ethylene and N1[ The rates at whichthe dihydrogen is displaced varies greatly with theacetonitrile and pyridine reactions being virtuallyinstantaneous while those involving ethylene or N1

take several hours[ A combination of infrared spec!trophotometry\ NMR specroscopy and X!ray crys!tallography con_rms that\ in most cases\ the _nalproduct takes the form trans!ðFe"H#"L#"h1!dppm#1ŁðBF3Ł as summarized in Scheme 0[

In certain cases "Scheme 0#\ additional reactionsoccur[ For example\ the outcome of protonation of 1

by HBF3 = Et1O "molar ratio 0]4# in acetonitrile is afunction of reaction time and temperature[ At !29>C\the only product is 2 while at room temperature themain product is 8\ with two trans acetonitrile ligands[However\ 20P NMR spectra reveal that\ initially\ threeproducts are present since signals due to 2\ 8 and athird component which shows two triplets centered atd 01[2 and 0[97 are observed[ This third component isbelieved to be cis!ðFe"CH2CN#1"dppm#1Ł ðBF3Ł1\ 09[The signals due to this component rapidly disappearfrom the spectrum as conversion of all components ofthe mixture into 8 occurs[ The largest amounts of thecis isomer\ 09\ obtainable in these experiments wereobserved "20P spectrum# to be formed in fresh solu!tions of 1 and HBF3 = Et1O "in a 0]4 molar ratio# inCH2CN[ Under these conditions\ the two isomers areformed in approximately equal amounts although therelative proportion of the trans isomer 8 still growsrapidly with time[ The Fe!dppm ring opening andrearrangement apparently required in the formationof the cis isomer from 1 or 2 may be facilitated by thereversible interaction of the excess of H¦ present witha P atom of dppm as has been observed ð09Ł in studies

Some reaction chemistry of trans!ðFe"H#"h1!H1#"h1!dppm#1Ł ðBF3Ł[ 2774

of the related reactions of ðFeHX"diphosphine#1Ł"X�Cl\ Br# under acid conditions[ The fact that 8 isproduced from 0 or 1 in the presence of excesses ofH¦ and CH2CN implies that hydride!protonation fol!lowed by H1 displacement is a stepwise process andthat after 2 is formed\ further protonation of itshydride ligand occurs\ as has been observed for theprocess trans!ðOs"H#"CH2CN#"dppe#1Ł¦ :trans!ðOs"H1#"CH2CN#"dppe#1Ł1¦ ð00Ł[ In the Fe case itseems that there is a second H1 for CH2CN exchange[This prompted an investigation of the protonation of1 with no H1!displacing ligand present[ It was foundthat protonation of 1 in THF or CH1Cl1\ or pro!tonation of 0 in CH1Cl1 or CD1Cl1\ under N1 or argon\or in THF under H1\ produced solutions which exhi!bited a single 20P NMR signal at d 2[2[ "Fe]HBF3

molar ratios ranged from 0]0 to greater than 0]09#[This signal is believed to be due to the bis"dihydrogen#complex 7 although repeated attempts to detect thedihydrogen signal in the 0H NMR spectrum wereunsuccessful due to interference from strongHBF3 = Et1O signals[ This complex appears to be rela!tively stable towards H1!displacing ligands in THFor CH1Cl1 in the presence of an excess of acid[ Forexample\ with a 09 fold molar excess of HBF3 present\these solutions react only very slowly with acetonitrileto produce 8\ although again the cis isomer is presentin the initial stages of the reaction[ These observationssupport the suggestion that in the direct synthesis of8 from 1\ the most likely intermediate is 2 rather than7[

In similar reactions involving protonation of a mix!ture of cis! and trans!ðRu"H#1"dppm#1Ł in CH2CNusing a large excess of HBF3\ only the cis isomer ofðRu"CH2CN#1"dppm#1Ł ðBF3Ł1\ characterized crys!tallographically\ was obtained ð01Ł[

All attempts to isolate solid 7 from solutions exhi!biting the d 2[2 signal in the 20P spectrum resulted inspontaneous deprotonation\ even under an atmo!sphere of H1\ and formation of 0[ This observation\in itself\ is good evidence that complex 7 is certainlya symmetrical dihydrogen complex and probably abis"dihydrogen# complex even though no dihydrogensignals are observable in the 0H NMR spectra undera variety of conditions[ The implication is that thesesignals are displaced from their usual positions andare masked by other solvent signals[

Other than a few species existing in solutions atvery low temperatures ð02Ł or in a matrix ð03Ł\ fewcomplexes containing two dihydrogen ligands areknown[ Among these are certain complexes of Ru ð04\05Ł\ Ir ð06Ł and Re ð05Ł\ some of which are preparedby protonating polyhydrides ð05Ł[ They are labile\ theIr complex\ for example\ being stable only at !79>Cunless kept under an atmosphere of H1[

Addition of ligands "other than acetonitrile# to solu!tions exhibiting the d 2[2 signal in the 20P spectrumresulted in deprotonation to give the correspondingmonosubstituted ðFeH"L#"dppm#1Ł¦ system and noother bis!substituted complexes analogous to 8 could

be obtained[ Neither could such complexes beobtained by further protonation of monohydridiccomplexes such as 4\ 5 and 6 in the presence of anexcess of the H1!displacing ligand[ It is possible inthese cases that\ after H1 in 0 is displaced by anotherligand\ a combination of the strong trans in~uence ofthe H! and the Lewis basic properties of the ligandleads to proton attack at another site in the molecule[

Considering now X!ray structural data for the com!plexes reported herein\ and related complexes in theliterature\ trans!ðFe"CH2CN#1"dppm#1Ł ðFeI3Ł = 1H1O\which contains the same cation as in 8\ has been pre!pared from FeI1"dppm#1 and CH2CN and structurallycharacterized by crystallography ð7Ł[ In addition\recent work ð07Ł has established that related com!plexes of the type trans!ðFeL1"PP#1Ł ðXŁ1 "L�variousnitriles including CH2CN\ PP�R1P"CH1#1PR1 withR�CH2 or C1H4\ and X�BF3 or PF5# can be syn!thesized either via protonation of FeH1"PP#1 followedby exchange of the resulting H1 ligand or from reac!tions of FeCl1"PP#1 with nitriles[ The structures ofseveral of these analogues of 8 were determined ð07Łby X!ray crystallography[ The structural parametersestablished by us for 8 itself are very similar to thosereported ð7Ł for trans!ðFe"CH2CN#1"dppm#1ŁðFeI3Ł = 1H1O and the published bond lengths for thelatter will be used for comparison purposes in thispaper[

Structural information has also been acquired for 2

and 3 although due to a very small crystal\ only themain structural features of 3 were con_rmed "suc!cinonitrile bound through one CN group trans to theH−! see experimental section#[ For 2\ the crystal\ datacollection and re_nement data are recorded in Table0 while appropriate bond lengths and angles are sum!marized in Table 1[ An ORTEP drawing showing theFe coordination geometry is shown in Fig[ 0[ The BF3

anion is disordered over three positions"9[39]9[23]9[15 ratio# related by rotation[ As in thestructures of the other complexes containing chelatingdppm\ distortions from octahedral geometry are duein large part to the strained 3!membered FePCP rings\with P!Fe!P angles of 62!63> and P!C!P angles ofabout 07> smaller than that required for a tetrahedralC atom[ These\ in turn\ determine the non!linearity ofthe trans P!Fe!P angles ð069[43"5# and 062[01"5#>Ł[ TheFe!H distance of 0[24"5# A� is shorter than the sum ofthe covalent radii of Fe and H and considerably shor!ter than Fe!H distances of 0[4!0[5 A� \ determined bothby X!ray and neutron di}raction methods\ found incomparable complexes ð3\ 08\ 19\ 10Ł[ This discrepancyis probably due to the di.culties in accurately locatingH atoms using X!rays\ and also re~ects the uncertaintyin the N!Fe!H angle of 061"2#> in 2[

In the acetonitrile ligand\ the N2C and the C!Cdistances are within the range found for analogouscompounds containing coordinated acetonitrile ð7\07Ł[ The most signi_cant observation with respect tothe coordinated CH2CN concerns the Fe!N bondwhich is longer in 2 ð0[816"3# A� Ł than in

Y[ Gao et al[2775

Table 0[ Crystal data and structure re_nement for trans!ðFe"H#"NCCH2#"dppm#1Ł ðBF3Ł "2#

Empirical formula C41H37BF3FeNP3"2#Formula weight 832[34Temperature "K# 182"1#Wavelength "A� # 9[60962Crystal system MonoclinicSpace group P10:naA� 01[414"2#bA� 06[794"3#cA� 10[439"3#b> 81[46"2#Volume "A� 2# 3688"1#Z 3Dcalc "g cm−2# 0[219Absorption coe.cient "mm−0# 9[388Crystal size "mm# 9[41×9[36×9[15Crystal description orange plateF"999# 0865Range "># 0[37 to 12[87Index ranges −03³�h³�03\9³�k³�19\ 9³�0³�13Re~ections collected 6497Independent re~ections 6497 ðR"int#�9[9999ŁRe_nement method Full!matrix least!squares on F1

Data:restraints:parameters 6497:9:464Goodness!of!_t on F1 9[847Final R indices� R0�9[9509\ wR1�9[0234

ð3452Fo×3s"Fo#ŁR indices "all data# R0�9[0937\ wR1�9[0234Largest di}[ peak and hole "e Aý−2# 9[388 and −9[219

�R0�s==Fo=−=Fc==:s=Fo=^wR1�ðsðw"F1o−F1

c#1Ł:sðw"F1

o#1ŁŁ9[4

Table 1[ Selected bond lengths ðA� Ł and angles ð>Ł for ðFe"H#"NCCH2#"dppm#1ŁBF3"2#

FeÐP"3# 1[192"1# P"3#ÐFeÐP"2# 63[05"4#FeÐP"2# 1[192"1# P"0#ÐFeÐP"1# 62[52"4#FeÐP"0# 1[195"1# N"0#ÐFeÐP"3# 85[77"01#FeÐP"1# 1[103"1# N"0#ÐFeÐP"2# 87[98"02#FeÐH"0# 0[24"5# N"0#ÐFeÐP"0# 80[25"02#FeÐN"0# 0[816"3# N"0#ÐFeÐP"1# 78[80"01#N"0#ÐC"2# 0[026"5# P"3#ÐFeÐH"0# 71"2#C"2#ÐC"3# 0[340"7# P"2#ÐFeÐH"0# 63"2#

P"0#ÐFeÐH"0# 86"2#P"1#ÐFeÐH"0# 81"2#P"3#ÐFeÐP"0# 093[88"5#P"2#ÐFeÐP"0# 069[43"5#P"3#ÐFeÐP"1# 062[01"5#P"2#ÐFeÐP"1# 095[94"5#N"0#ÐFeÐH"0# 061"2#P"0#ÐC"0#ÐP"1# 89[7"1#P"2#ÐC"1#ÐP"3# 81[0"1#

ðFe"CH2CN#1"dppm#1Ł ðFeI3Ł = 1H1O ð0[756"01# A� Ł dueto the strong trans in~uence of the H− in 2[

The Fe!P bond lengths decrease signi_cantly\ from1[205"2#!1[189"1# A� in trans!ðFeCl"CO#"dppm#1Ł ðBF3Łto 1[174"3#!1[170"3# A� in ðFe"CH2CN#1"dppm#1Ł

ðFeI3Ł = 1H1O to 1[103"1#!1[192"0# A� in 2 to 1[061"1#!1[042"1# A� in 1[ Since the s!bonding capabilities of thetrans ligands increase in this order\ it is possible thatthe corresponding strengthening of the Fe!P bond isassociated with a greater involvement of Fe!P p back!

Some reaction chemistry of trans!ðFe"H#"h1!H1#"h1!dppm#1Ł ðBF3Ł[ 2776

Fig[ 0[ ORTEP drawing of 2[

bonding as electron density is redistributed from theFe[ It is also possible that the size of the groups in theaxial positions in~uence the Fe!P bond lengths\ withthe smallest axial groups resulting in the shortest Fe!P bonds[ Since several factors a}ect the chemical shiftsof the P atoms\ it is di.cult to correlate d values of09[2\ 03 "in 8#\ 29 and 13\ respectively\ with structuralparameters "see also below#[

Selected spectroscopic data are summarized inTable 2 for the compounds containing the trans L!Fe!H arrangement reported herein together with data forthe related structures trans!ðFe"H#"Cl#"dppm#1Ł andtrans!ðFe"H#"CO#"dppm#1Ł ðBF3Ł ð3Ł[ There has beenconsiderable discussion in the literature regarding theextent to which metal ions undergo p!back bondingto a dihydrogen ligand[ It was hoped that the aboveseries of compounds would allow changes in thesespectral parameters to be related to changes in the Fe!ligand bonding pattern[ In each case\ the singlet in the20P nmr spectrum\ and the up_eld quintet in the 0Hspectrum are consistent with the trans H!Fe!Larrangement[ yFe!H varies widely as would beexpected from the large di}erences in the measured

Table 2[ Selected spectroscopic properties of trans!ðFe"H#"L#"dppm#1Ł¦ cations

Complex 2 3 4 5 6 1 0

L C0a MeCN succ py C1H3 N1 Ha COa H1a

yFeÐHb 0778 0779 0770 0742 0603 0602 0600 0609 0697d0Hc −10[1 −02[9 −02[0 −06[9 −0[7 −8[3 −6[9 −1[9 −6[1d20Pc 13[1 18[7 29[2 11[6 21[7 13[1 13[9 20[5 21[4

a ref[ ð3Łbcm−0\ some signals very weak^cCD1Cl1 or CH1Cl1\ room temp[

Fe!H bond lengths ð0[24"5# A� for 2 and 0[45"7#\0[47"7# A� for 1Ł[ It is apparent that the IR and 0HNMR data fall into two categories[ First\ when the Feis coordinated to any of the four predominantly weaks donor ligands "each with a relatively weak transin~uence#\ the trans hydride is also strongly bound"highest yFe!H\ 0742!0778 cm!0# and highly shielded[In the second group\ which contains the strong s

donor H! and the good p acceptors CO and C1H3 "allof which have a strong trans in~uence relative to thecorresponding ligands in the _rst group#\ yFe!H valuesindicate a weaker Fe!H bond[ The hydride ligandstrans to the good p acceptors are also the most desh!ielded[ It appears that N1 behaves in a similar way toC1H3 and CO in that there is a signi_cant s!p inter!action as evidenced by the weakening of the N1 bond"yN1 reduced from 1220 in N1 to 1005 cm!0 in 6#[ Thesurprising strength of the N1!Fe interaction is illus!trated by the fact that\ as mentioned earlier\ N1 dis!places pyridine from 4 "rapidly# and C1H3 "slowly#from 5[ The Fe!H bond in 0 appears comparable instrength to others in this second group of complexes\also suggesting a s!p interaction in these complexesconsistent with the lengthening of the H!H bond from9[7 A� in H1 to\ for example\ 9[81 A� in 0 as calculatedð3Ł from JHD values[ Previous work ð3Ł interpretedthe position of yFe!H in 1 as being due to the transin~uence[ It should also be noted that the H1 ligandin 0 has little e}ect upon the electronic environmentof the trans H! compared to those in 1 and this explainswhy this remaining H is as susceptible to protonationas are those on the dihydride[

As noted above\ there is no discernible relationshipbetween the trans ligands in the various complexes andthe phosphorus chemical shifts which are generallytypical of P in 3!membered rings[

Acknowled`ements*We thank the Natural Sciences andEngineering Research Council of Canada and the LakeheadUniversity Senate Research Committee for _nancial support[We thank also G[ P[ A[ Yap of the University of WindsorMolecular Structure Centre for the X!ray determination ofthe structure of complex 3 and both C[ Lundeen "UMD# andV[ G[ Young\ Jr[ "University of Minnesota CrystallographicLaboratory# for the determination of the structure of 8[ Areferee made several helpful suggestions[

Y[ Gao et al[2777

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