BINUCLEAR PALLADIUM COMPLEXES WITH BRIDGING HYDRIDES - UNUSUAL COORDINATION BEHAVIOR OF LIBET(4) AND NABET(4)

The reaction of Pd(dippp)Cl-2 (dippp = 1,3-bis(diisopropylphosphino)propane) with a 1:1 mixture of LiBEt(2)H(2) and LiBEt(4) in THF generates the binuclear hydride derivative [(dippp)Pd](2)(mu-H)(2).LiBEt(4) (1) in which the LiBEt(4) is bound to the palladium hydride core. The bare palladium hydride dimer [(dippp)Pd](2)(mu-H)(2) (2) was prepared by reaction of 2 equiv of KBEt(3)H in toluene with Pd(dippp)I-2. Addition of LiBEt(4) to the bare palladium dimer 2 generates the LiBEt(4) adduct 1; this approach has been extended to the preparation of [(dippp)Pd](2)(mu-H)2.NaBEt(4) (3) and [(dippp)Pd](2)(mu-H)(2).LiAlEt(4) (4) by the addition of NaBEt(4) and LiAlEt(4) respectively to 2. On the basis of NMR spectroscopy, there is no evidence for dissociation of the lithium of sodium berate or aluminate salts from the hydride dimer but the ME'Et(4) (M = Li, Na; E' = B, Al) units are labile on the basis of exchange studies and variable temperature NMR data. Crystals of [(dippp)Pd](2)(mu-H)(2).LiBEt(4)0.5(C6H14) (1) are monoclinic, a = 11.537(2) Angstrom, b = 19.114(2) Angstrom, c = 24.020(1) Angstrom, beta = 98.674(9)degrees, Z = 4, space group P2(1)/n; those of [(dippp)Pd](2)(mu-H)(2) (2) are monoclinic, a = 13.128(1) Angstrom, b = 14.362(4) Angstrom, c = 20.353(1) Angstrom, beta = 99.593(6)degrees, Z = 4, space group P2(1)/n; and those of [(dippp)-Pd](2)(mu-H)(2).NaBEt(4) (3) are monoclinic, a = 20.099(2) Angstrom, b = 11.457(5) Angstrom, c = 21.600(3) Angstrom, beta = 92.87(1)degrees, Z = 4, space group P2(1)/c. The structures were solved by the Patterson method and were refined by full-matrix least-squares procedures to R = 0.033, 0.052, and 0.033 (R(W) = 0.029, 0.054, and 0.028) for 5954, 4560, and 5018 reflections with I greater than or equal to 3 sigma(I), respectively. In the solid-state structure of 1, there are three C-H...Li interactions from the ethyl groups attached to boron whereas in the solid-state structure of 3 there are four such C-H...Na interactions.