2920Organometallics,Vol.29,No.13,2010

Scheme3.SyntheticPathwaysfortheBisosmabenzenes9a-dBridgedbyDiisocyanide

Ligands

Huangetal.

evenunderrefluxovernightandcanbestoredatroomtemperatureforatleastamonthwithoutdecompositioninaninertatmosphere.

Complexes9a-dhavealsobeencharacterizedbyelemen-talanalysis,IR,andmultinuclearNMRspectroscopy.Alldataarefoundtobeconsistentwithexpectations.SelectedNMRandIRdataareshowninTable1.

AsshowninTable1,9a-dexhibitNMRsignalswithsimilarchemicalshiftsandcouplingconstants,whichisconsistentwiththeirnearlyidenticalligandenvironmentsaroundtheOsmetalcenters.The31P{1H}NMRspectrashowtwosingletsintherangesδ=17.00-18.68ppm(CPPh3)and-2.12to-5.18ppm(OsPPh3),respectively.Inthe1HNMRspectrum,eachofthecomplexes9a-dshowsasingletintherangeδ=16.52-16.68ppmandadoubletatδ=13.63-13.77ppmwithaH-Pcouplingconstantofapproximately29.0HzforOsCHCClandOsCHCPPh3,respectively.Thepara-protonstothemetalcentersontheringgiveadoubletatδ=7.56-7.83ppmwithaH-Pcoupl-ingconstantofapproximately13.3Hz.Theprotonsontheringsoppositethephosphoniumgroupsaremoredownfieldcomparedwiththoseattheortho-positioninthecomplexes9a-d.Thiseffectwasalsoobservedforourpreviouslyreportedmetallabenzeneswithonephosphoniumgrouponthecarbonatomofthemetallacycles.5k,l,n,21The13CNMRspectrademonstratesimilartrends,thatthesignalsforcarbonatomsontheosmabenzeneringsresonateintherangeδ=232.45-233.40(OsCHCPPh3),251.70-265.09(OsCHCCl),136.34-136.42(CCl),115.35-116.04(CPPh3),and139.28-139.58(CClCH)ppm,respectively.Overall,complexes9a-ddisplayaconsiderablyupfieldshiftinresonancesincompari-sonto5a,bduetothepresenceofonlyonephosphoniumgrouponthemetallacycle,whichdecreasestheelectroniceffect.

Inaddition,theisocyano-carbonsignalsappearintherangeδ=141.78-156.22ppm.TheFTIRspectraof9a-dexhibitastrongIRabsorptionintherangeν=2064-2086cm-1fortheCtNtriplebond,whichundergoesanabout30cm-1shifttolowerfrequencycomparedwiththoseofthefreeligandsprobablyduetotheM-Cπ-bondinginteraction.20b,24

Repeatedeffortstogrowcrystalsof5a-dand7wereunsuccessful.However,wedidobtaingood-qualitycrystalsfor9d.Thestructureofcomplex9dhasbeenunambiguously

(24)Swanson,S.A.;McClain,R.;Lovejoy,K.S.;Alamdari,N.B.;Hamilton,J.S.;Scott,ngmuir2005,21,5034.

establishedbysingle-crystalX-raydiffraction.ApreliminarythermalellipsoiddrawingofthedicationisshowninFigure1.Itconfirmsthatcomplex9dindeedcontainstwosix-mem-beredmetallacyclesconnectedbya1,4-phenylenediisocyanidebridge.Thismoleculeiscentrosymmetric,andthustheasym-metricalunitofthisstructurecontainshalfamolecule.Eachmetallacyclecontainsaphosphoniumandachlorosubstitu-entatC2andC4,respectively.ThemetallabenzeneringconsistingofOs1/C1/C2/C3/C4/C5isalmostcoplanar,which

)fromthermsplanesofisreflectedbythedeviation(0.0471A

thebestfit,andthemetallacycleisalmostperpendiculartothebenzeneringof1,4-phenylenediisocyanidewiththedihe-dralanglebetweenthemetallabenzeneringandthebridgingbenzeneringof98.1°.ThebonddistancesforOs1-C1

),C1-C2(1.383(7)A),C2-C3(1.424(7)A),(2.046(5)A

),C4-C5(1.401(8)A),andOs1-C5C3-C4(1.366(7)A

),togetherwiththoseforOs1-P1(2.4013(12)A)(1.952(5)A

),areconsistentwiththoseofourandOs1-Cl1(2.5048(13)A

previouslyreportedosmabenzenesderivatives.5nAsexpected,

)bondisshorterthantypicalOs-CtheOs1-C01(1.979(5)A

)islongerthanthesinglebonds,whereasC01tN1(1.159(6)A

freeCtNtriplebond,showingsubstantialπ-back-bondingcontributionfromthemetalcentertotheisocyanideligand.19a,25TheOs-CtNbondangleof168.7°isclosetolinearity.Thesolid-statestructureof9disconsistentwithitsspectroscopicdatasummarizedinTable1.Asmentionedabove,the31P{1H}NMRspectrumshowstheCPPh3signalatδ=18.67ppmandtheOsPPh3signalatδ=-2.12ppm,respectively.The1HNMRspectrumshowsasingletatδ=16.52ppmfortheOsCHCClandadoubletatδ=13.63ppmfortheOsCHC-(PPh3),whereasinthe13C{1H}NMRspectrumthemetalla-cyclecarbonsignalsareobservedat233.01(C1),116.04(C2),139.58(C3),136.34(C4),and251.89(C5)ppm,respectively.Additionally,theCtNstretchforthebismetallabenzene9doccursatν=2064cm-1,somewhatlowerinenergythanthatofthefree1,4-phenylenediisocyanideligand(ν=2118cm-1).24

Mechanistically,formationofthediisocyanide-bridgedosmabenzenes9a-dfromthereactionsshowninScheme3issimilartotheformationofthemonophosphonium-sub-stitutediodo-aswellasthiocyanato-osmabenzenes,which

(25)(a)Rickard,C.E.F.;Roper,W.R.;Williamson,A.;Wright,anometallics1998,17,4869.(b)Clark,G.R.;Waters,J.M.;Whittle,K.R.J.Chem.Soc.,DaltonTrans.1976,2029.(c)Johnson,T.W.;Tetrick,S.M.;Fanwick,P.E.;Walton,R.A.Inorg.Chem.1991,30,4146.(d)Cheung,W.-M.;Zhang,Q.-F.;William,I.D.;Leung,W.-H.Inorg.Chem.2007,46,5754.