113509-37-8Relevant articles and documents
Palladium(0) complexes formed by a chelating olefinic tertiary phosphine. Synthesis, fluxional behavior, and X-ray crystal structure of Pd(o-CH2=CHC6H4PPh2)2, a three-coordinate complex containing a weak interaction between the metal atom and an α-vinylic hydrogen atom
Bennett, Martin A.,Chiraratvatana, Chindarat,Robertson, Glen B.,Tooptakong, Uncharee
, p. 1403 - 1409 (2008/10/08)
Reaction of Pd(η3-C3H5) (η5-C5H5) with exactly 2 mol equiv of (2-vinylphenyl)diphenylphosphine (o-styryldiphenylphosphine, o-CH2=CHC6H4PPh2, abbreviated SP) gives the zerovalent palladium complex Pd(SP)2 (4). The reaction proceeds via a thermally unstable intermediate, Pd(C3H5)(C5H5)(SP) (3), which can be isolated from the reaction of Pd(η3-C3H5)(η5-C 5H5) with SP at -70°C. Crystals of 4 are triclinic, space group P1, with a = 21.456 (3) A?, b = 9.483 (2) A?, c = 9.202 (2) A?, α = 60.84 (1)°, β = 87.67 (1)°, γ = 81.12 (2)°, and Z = 2. The structure was solved by heavy-atom methods and refined by least-squares methods to R = 0.032 and Rw = 0.036 for 5536 independent reflections. In contrast to Ni(SP)2 and Pt(SP)2, which are tetrahedral, crystalline 4 adopts an approximately trigonal-planar structure, one SP ligand being bidentate and the other being bound through phosphorus only. There is also a weak agostic interaction between the palladium atom and the α-hydrogen atom H(19) of the uncoordinated vinyl group. With the assumption of a C(19)-H(19) bond length of 1.08 A?, the Pd-H(19) distance is calculated to be 2.46 A?. The coordinated vinyl group is displaced markedly from the trigonal plane, the dihedral angle between the planes P(1)-Pd-P(2) and C(39)-Pd-C(40) being 24.7 (2)°, and is bound asymmetrically, the distances to the terminal and inner carbon atoms being 2.213 (4) A? and 2.141 (3) A?, respectively. The Pd-P bond lengths are equal [Pd-P(1) = 2.3029 (7) A?, Pd-P(2) = 2.3054 (7) A?], and the C=C distances in the free and coordinated vinyl groups are 1.293 (5) and 1.387 (5) A?, respectively. The variable-temperature 31P{1H} NMR spectrum of 4 at -80°C shows that the trigonal complex 4a, which has inequivalent phosphorus atoms, coexists with a species 4b containing equivalent phosphorus atoms; the proportion of 4b increases at -50°C. 4b is suggested to be a two-coordinate complex in which both vinyl groups interact weakly with the palladium atom. Above -50°C 4a and 4b equilibrate rapidly on the NMR time scale leading to equivalence of the free and coordinated vinyl groups. 4 reacts with additional SP to give Pd(SP)3 (5), in which all the vinyl groups are free, and with aqueous HBF4 to give the five-membered ring chelate (σ-alkyl)palladium(II) salt trans-[Pd(o-CH3CHC6H4PPh 2)(SP)]BF4 (6). Comparison of the properties of the M(SP)2 complexes (M = Ni, Pd, Pt) confirms that olefin binding is weakest in the palladium compound.
