Hydride Transfer to Gold: Yes or No? Exploring the Unexpected Versatility of Au...H-M Bonding in Heterobimetallic Dihydrides

The potential for coordination and H-transfer from Cp2MH2(M=Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au](+)cations react with Cp(2)WH(2)giving [(L)Au(kappa(2)-H2WCp2)](+)(L=IPr (1), cyclic (alkyl)(amino)carbene (2), PPh3(3) and Dalphos-Me (4) [IPr=1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me=di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP)(2)](+)(DMAP=p-dimethylaminopyridine) affords theC(2)-symmetric [Au(kappa-H2WCp2)(2)](+)(5). The Dalphos complex 4can be protonated to give the bicationic adduct4 H,showing Au-I...H+-N hydrogen bonding. The gold(III) Lewis acid [(C<^>N-CH)Au(C6F5)(OEt2)](+)binds Cp(2)WH(2)to give an Au-H-W sigma-complex. By contrast, the pincer species [(C<^>N<^>C)Au](+)adds Cp(2)WH(2)by a purely dative W -> Au bond, without Au...H interaction. The biphenylyl-based chelate [(C<^>C)Au](+)forms [(C<^>C)Au(mu-H)(2)WCp2](+), with two 2-electron-3-centre W-H...Au interactions and practically no Au-W donor acceptor contribution. In all these complexes, strong but polarized W-H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp(2)ZrH(2)with gold complexes led in all cases to rapid H-transfer and formation of gold hydrides. Relativistic DFT calculations were used to rationalize the striking reactivity and bonding differences in these heterobimetallic hydride complexes along with an analysis of their characteristic NMR parameters and UV/Vis absorption properties.