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)pr opane) with a 1:1 mixture of LiBEt(2)H(2) and LiBEt(4) in THF generate s 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 ba re 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. Additio n of LiBEt(4) to the bare palladium dimer 2 generates the LiBEt(4) add uct 1; this approach has been extended to the preparation of [(dippp)P d](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 basi s of NMR spectroscopy, there is no evidence for dissociation of the li thium of sodium berate or aluminate salts from the hydride dimer but t he 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 [(dipp p)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 = 98.6 74(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) Angstro m, 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 monoc linic, a = 20.099(2) Angstrom, b = 11.457(5) Angstrom, c = 21.600(3) A ngstrom, beta = 92.87(1)degrees, Z = 4, space group P2(1)/c. The struc tures were solved by the Patterson method and were refined by full-mat rix 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 gre ater than or equal to 3 sigma(I), respectively. In the solid-state str ucture of 1, there are three C-H...Li interactions from the ethyl grou ps attached to boron whereas in the solid-state structure of 3 there a re four such C-H...Na interactions.