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

Abstract

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(κ 2 -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(μ-H)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.

Hydridotetrylene [Ar*EH] (E = Ge, Sn, Pb) coordination at tantalum, tungsten, and zirconium

“…Rocchigian, Bochmann and Hrobárik et al reported recently on the different coordination modes of Cp2WH2 at Au(I)/Au(III) cations. 61 In the case of asymmetric hydride coordination a comparable 1 H NMR spectrum was observed: -11.4 ppm, JW-H 48 Hz, -9.6 ppm, JW-H 61 Hz. 61 Furthermore, chemical exchange of all hydrides in cations 3 was proven by 1 H-1 H EXSY NMR studies.…”

“…61 In the case of asymmetric hydride coordination a comparable 1 H NMR spectrum was observed: -11.4 ppm, JW-H 48 Hz, -9.6 ppm, JW-H 61 Hz. 61 Furthermore, chemical exchange of all hydrides in cations 3 was proven by 1 H-1 H EXSY NMR studies. For the characterization of the isomers by 119 Sn, 207 Pb and 183 W NMR spectroscopy see Table 1 and the SI.…”

Recent Advances in Gold(III) Chemistry: Structure, Bonding, Reactivity, and Role in Homogeneous Catalysis

“…In agreement with this, no reaction occurred between H 2 (1 bar, −10 °C) and ether-free 30. However, with the ether adduct 28 H−H cleavage takes place within a few hours at −20 °C, via an [LAu + 216 In addition to these σ-bonded species formed en-route to H−E bond activation, the question whether gold compounds are able to form hydrogen bonds of the type D−H (+) •••M has attracted significant attention recently. 217−222 In such arrangements D is an electron-rich donor atom covalently bonded to H, and M possesses an electron pair capable of acting as proton acceptor, to give a 4-electron-3-center interaction.…”

“…Relativistic DFT calculations showed the presence of electron density along the Au–W vector of 64 and its absence in the case of 65 . The calculations also showed that in all of these gold hydride complexes the W–H bond is polarized but remains present and strong, while true covalent Au–H bonds are not yet formed …”

The Elusive Au(I)···H–O Hydrogen Bond: Experimental Verification

“… The Lewis basic behavior that gold displays in such complexes is further illustrated by the recent demonstration that adequately substituted gold­(I) centers are prone to protonation or amenable to the formation of Au···H-X HBs (HB = hydrogen bond, X = electronegative element) . The formation of Au···H–X interactions was originally supported by calculations as in the case of C , and later experimentally verified for cationic derivatives such as D and E . − The stability of such HBs benefits from the metallobasic character of gold as well as its electronegativity, which strengthens the charge transfer and Coulombic term of the Au···H–X interaction, respectively. Dispersion forces, enhanced by relativistic effects at gold, are also invoked as substantial contributors…”