Dinuclear palladium complexes with bridging hydrides

The palladium hydride dimer, [(dippp)Pd]₂(µ--H)₂, (2) (dippp = 1,3-bis(diisopropylphosphino)propane), was synthesized, and its interaction with lithium tetraethylborate examined. When the two compounds were mixed in stoichiometric amounts high yields of the adduct, [(dippp)Pd]₂(µ-H) ₂•LiBEt₄ (1) — previously isolated adventitiously by a co-worker — were obtained. Variable temperature ³¹P{¹H} NMR spectroscopy showed a condition of chemical equilibrium between 2 and 1, but the value of the equilibrium constant, Keq, could not be determined owing to its large magnitude. Extension of this chemistry to other sources of Li⁺ led to the isolation of the aluminate adduct, [(dippp)Pd]₂((µ-H)₂,•LiA1Et₄ (3). Likewise when NaBEt₄ was substituted an adduct formulated as [(dippp)Pd]₂(µ-H)₂•NaBEt₄ (4) was obtained. The interaction of tetraethylborate salts with other transition-metals was also examined, with evidence of adduct formation for both [(dippp)Rh]₂(µ-H)₂ and [(dippp)Ni]₂(µ-H)₂ (6) with LiBEt₄. It was not possible to isolate these compounds as analytically pure samples. This general interaction is discussed in terms of metal basicity. The reactivity of 2 towards organic donor species was also studied. Addition of excess donor results in the formation of tricoordinate Pd(0) species: (dippp)Pd(ɳ²-H₂C=CH₂) (5), (dippp)Pd(PPh₃) (7), and (dippp)Pd(DMAD) (8) (DMAD = dimethylacetylenedicarboxylate) were thus isolated. When a stoichiometric equivalent of donor was added to 2, no dimeric intermediates could be observed.Science, Faculty ofChemistry, Department ofGraduat