Solution Chemistry of a Water-Soluble η²-H₂Ruthenium Complex:  Evidence for Coordinated H₂Acting as a Hydrogen Bond Donor

Abstract

The ability of an eta2-H2 ligand to participate in intermolecular hydrogen bonding in solution has long been an unresolved issue. Such species are proposed to be key intermediates in numerous important reactions such as the proton-transfer pathway of H2 production by hydrogenase enzymes. We present the synthesis of several new water-soluble ruthenium coordination complexes including an eta2-H2 complex that is surprisingly inert to substitution by water. The existence of dihydrogen hydrogen bonding (DHHB) was experimentally probed by monitoring the chemical shift of H-bonded Ru-(H2) complexes using NMR spectroscopy, by UV-visible spectroscopy, and by monitoring the rotational dynamics of a hydrogen-bonding probe molecule. The results provide strong evidence that coordinated H2 can indeed participate in intermolecular hydrogen bonding to bulk solvent and other H-bond acceptors.

Bis{1,2-bis[bis(3-methoxypropyl)phosphanyl]ethane-κ2P,P′}dichloridoosmium(II)

“…For background to transition-metal dihydride complexes, see: Egbert et al (2007); Heinekey et al (2004); Miller et al (2002); Szymczak & Tyler (2007); Szymczak et al (2006).…”

“…(DMeOPrPE is the watersoluble, bidentate phosphine ligand 1,2-bis(bis(methoxypropyl)phosphanyl)ethane.) In prior work, we synthesized transFe(DMeOPrPE) 2 (H 2 )H + and trans-Ru(DMeOPrPE) 2 (H 2 )H + by reaction of the trans-M(DMeOPrPE) 2 Cl 2 complexes with H 2 (Miller et al, 2002, Szymczak et al, 2006. In order to synthesize the analogous H 2 complex of Os, we synthesized the trans-Os(DMeOPrPE) 2 Cl 2 complex reported here.…”

(Ethane-1,2-diyl)bis[bis(3-methoxypropyl)methylphosphonium] bis(tetraphenylborate) diethyl ether solvate

“…For related literature, see: Churchill et al (1990); ; Gilbertson et al (2005Gilbertson et al ( , 2007; Miller et al (2002); Szymczak et al (2007); van der Sluis & Spek (1990).…”

“…The strong donating ability of this ligand allows these complexes to bind weakly coordinating molecules such as H 2 and N 2 (Gilbertson et al, 2007;Szymczak et al, 2007)). The DMeOPrPE ligand also imparts diverse solubility; often the complexes are soluble in solvents ranging from hexane to water.…”

A quantitative measure of the ionicity of selected iron hydride species by examination of the deuterium quadrupole coupling constant (DQCC)

“…A fourth, more direct assessment of hydride basicity or, more correctly, hydride ionicity is by reference to the deuterium quadrupole coupling constant (DQCC) of the metal hydride, whose magnitude may be easily determined by T 1 measurement of the corresponding metal deuteride, and the value so obtained is manipulated to give an estimate of hydride ionicity [9]. Measurement of DQCC for Mo, W, Zr, Mn, Re, Os and Rh metal hydrides has been made previously, where the metal centres possess standard octahedral geometries, and the hydride ligands have been trans to different ligands; DQCC values for bridging deuterides in rhenium carbonyl clusters has been the subject of a recent work [10], and have also been used as evidence for intermolecular hydrogen bonding to an g 2 -bound dihydrogen ligand [11]. Here, DQCC values of a series of iron hydrides, supported by chelating phosphines in octrahedral array, are measured and assessed, and thus information about the Fe-D bonding mode and, by extension, the Fe-H bond becomes available for comparison.…”