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 Cp₂WH₂ giving [(L)Au(κ²-H₂WCp₂)]⁺ (L = IPr (1), cyclic (alkyl)(amino)carbene (2), or phosphines 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 the C₂-symmetric [Au(κ-H2WCp2)2]⁺ (5). The Dalphos complex 4 can be protonated to give the bicationic adduct 4H, showing Au(I)…H+-N hydrogen bonding. The gold(III) Lewis acid [(C^N-CH)Au(C₆F₅)(OEt₂)]+ binds Cp₂WH₂ to give an Au-H-W σ-complex. By contrast, the pincer species [(C^N^C)Au]⁺ adds Cp₂WH₂ by a purely dative W→Au bond, without Au···H interaction. The biphenyl-based chelate [(C^C)Au]⁺ forms [(C^C)Au(µH)₂WCp₂]⁺, with two 2-electron-3-centre W-H…Au interactions and practically no Au-W donor acceptor contribution. In all these complexes strong but polarised W-H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp₂ZrH₂ 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.