ArticleOrganometallics,Vol.29,No.13,20102921

wereportedpreviously.5n,21AsdescribedinScheme4,com-plex8caninitiallyreactwithdiisocyanideinthepresenceofNH4PF6togivethediisocyanide-bridgedintermediateA,whichundergoesnucleophilicattackoftheCl-attheco-ordinatedalkyne,followedbyeliminationofanOH-fromtheγ-carbonatomtogivecomplexes9a-d.Infact,inourpreviousinvestigationontherelatedreactionofcomplex8withNaCl,wecouldalsodetecttheformationofmonopho-sphonium-substitutedchloro-osmabenzene,yetthereactionisnotclean,andourattempttoobtainpuresamplefromthecrudeproductsfailedprobablyduetotherelativelyweaknucleophilicityofchlorideionandthereadydecompositionofcomplex8andtheformedchloro-osmabenzeneinsolu-tion.5nItiswellknownthatisocyanideisagoodπ-acidicligand;thusreplacementofachlorideligandin8willdecreasetheelectrondensityofthemetalcenterandthecoordinatedalkyne,whichfacilitatesthenucleophilicattackatthecoordinatedalkynebythechlorideion.

ElectrochemicalStudies.Whilemanytheoreticalstudiesandvarioussyntheticmethodsofmetallabenzeneshavebeenreported,theelectrochemicalstudiesofmetallabenzenesarestillratherlimited.Tothebestofourknowledge,ourrecent

studiesontheelectrochemicalpropertiesofaseriesofruthe-nabenzenesandosmabenzenesandtheiranaloguesaretheonlyreportedexamples.5n,9,10Ofparticularinterestistheelectroniccommunicationbetweenthetwometalcentersobservedinthetrichloro-bridgedbisruthenabenzenes9andbisosmanaphalenes.10

Onthebasisofourfacilepreparationstrategyofthediisocyanide-bridgedbismetallabenzenesmentionedabove,wealsointendedtostudytheirelectrochemicalproperties.However,complexes5a-dand7couldslowlydecomposeinsolutiontogiveamixtureofundentifiedproducts.Wethushaveinvestigatedtheredoxbehaviorsofthestablebisme-tallabenzenes9a-d(1mMinCH2Cl2)bycyclicvoltammetry(CV)anddifferentialpulsevoltammogramtechniques(DPV)with0.1Mn-Bu4NClO4asthesupportingelectrolyte.ThevaluesofthepotentialsforthesecomplexesarepresentedinTable2,andtypicalCVsofcomplexes9a-daredisplayedinFigures2-5.

AsshowninFigures2and3,theCVandDPVofcomplex9aexhibitonequasi-reversibleoxidationwaveatEp,a=þ1.22Vpresumablyattributedtotheoxidationoftheosmiumcenter.Thisresultindicatesthatthereislittle

if