Structural, spectroscopic, and electronic features of weak hydrogen-bonded complexes of CpM(CO)(3)H (M = Mo (1a), W (1b)) hydrides with organic bases (phosphine oxides R(3)PO (R = n-C(8)H(17), NMe(2)), amines NMe(3), NEt(3), and pyridine) are determined experimentally (variable temperature IR) and computationally (DFT/M05). The intermediacy of these complexes in reversible proton transfer is shown, and the thermodynamic parameters (DeltaH degrees , DeltaS degrees ) of each reaction step are determined in hexane. Assignment of the product ion pair structure is made with the help of the frequency calculations. The solvent effects were studied experimentally using IR spectroscopy in CH(2)Cl(2), THF, and CH(3)CN and computationally using conductor-like polarizable continuum model (CPCM) calculations. This complementary approach reveals the particular importance of specific solvation for the hydrogen-bond formation step. The strength of the hydrogen bond between hydrides 1 and the model bases is similar to that of the M-H...X hydrogen bond between 1 and THF (X = O) or CH(3)CN (X = N) or between CH(2)Cl(2) and the same bases. The latter competitive weak interactions lower the activities of both the hydrides and the bases in the proton transfer reaction. In this way, these secondary effects shift the proton transfer equilibrium and lead to the counterintuitive hampering of proton transfer upon solvent change from hexane to moderately polar CH(2)Cl(2) or THF.

Reaction of the acidic tungsten(II) hydride 2 with the nickel(II) pincer complex 1 in either THF or toluene after an initial dihydrogen bonding (DHB) interaction led to the formation of the Ni–W bimetallic species 3 (see picture). The first example of DHB between two metal hydrides with opposite polarity was analyzed by NMR and IR spectroscopy, X‐ray crystallography, and DFT calculations.

a b s t r a c tCompound trans-PtBr 2 (C 2 H 4 )(NHEt 2 ) (1) has been synthesized by Et 2 NH addition to K[PtBr 3 (C 2 H 4 )] and structurally characterized. Its isomer cis-PtBr 2 (C 2 H 4 )(NHEt 2 ) (3) has been obtained from 1 by photolytic dissociation of ethylene, generating the dinuclear trans-[PtBr 2 (NHEt 2 )] 2 intermediate (2), followed by thermal re-addition of C 2 H 4 , but only in low yields. The addition of further Et 2 NH to 1 in either dichloromethane or acetone yields the zwitterionic complex trans-Pt (À) Br 2 (NHEt 2 )(CH 2 CH 2 N (þ) HEt 2 ) (4) within the time of mixing in an equilibrated process, which shifts toward the product at lower temperatures (DH ¼ À6.8 AE 0.5 kcal/mol, DS ¼ 14.0 AE 2.0 e.u., from a variable temperature IR study). 1 H NMR shows that free Et 2 NH exchanges rapidly with H-bonded amine in a 4$NHEt 2 adduct, slowly with the coordinated Et 2 NH in 1, and not at all (on the NMR time scale) with Pt-NHEt 2 or eCH 2 CH 2 N (þ) HEt 2 in 4. No evidence was obtained for deprotonation of 4 to yield an aminoethyl derivative trans-[PtBr 2 (NHEt 2 ) (CH 2 CH 2 NEt 2 )] À (5), except as an intermediate in the averaging of the diasteretopic methylene protons of the CH 2 CH 2 N (þ) HEt 2 ligand of 4 in the higher polarity acetone solvent. Computational work by DFT attributes this phenomenon to more facile ion pair dissociation of 5$Et 2 NH 2 þ , obtained from 4$Et 2 NH, facilitating inversion at the N atom. Complex 4 is the sole observable product initially but slow decomposition occurs in both solvents, though in different ways, without observable generation of NEt 3 . Addition of TfOH to equilibrated solutions of 4, 1 and excess Et 2 NH leads to partial protonolysis to yield NEt 3 but also regenerates 1 through a shift of the equilibrium via protonation of free Et 2 NH. The DFT calculations reveal also a more favourable coordination (stronger PteN bond) of Et 2 NH relative to PhNH 2 to the Pt II center, but the barriers of the nucleophilic additions of Et 2 NH to the C 2 H 4 ligand in 1 and of PhNH 2 to trans-PtBr 2 (C 2 H 4 )(PhNH 2 ) (1a) are predicted to be essentially identical for the two systems.

The interaction of CpM(CO)3H (M = Mo, W) hydrides as proton donors with different bases (B = pyridine, (n-Oc)3PO, ((CH3)2N)3PO, H3BNEt3) was studied by variable temperature IR spectroscopy and theoretically by DFT/B3LYP calculations. The data obtained show for the first time the formation of intermolecular hydrogen bonds between the neutral transition metal hydrides and bases in solutions of low polarity. These M-H...B hydrogen bonds are shown to precede the hydrides' deprotonation.