Bidentate Chelate Complexes Of Palladium(Ii) With The Carbanion 2-C6f4pph2 And Their Transformation Into Complexes Containing Bridging 2-C6f4pph2

Reaction of the organotin compound 2-Me3SnC6F4PPh2 (7) with the cycloocta-1,5-diene complexes [PdX2(cod)] at room temperature gives dinuclear halide-bridged palladium(H) complexes [Pd-2(mu-X)(2)(kappa(2)-2-C6F4PPh2)(2)] [X = Cl (5), Br (8)] in which the carbanions are present as four-membered chelate rings. The bridging halides can be replaced by various anions, giving the corresponding dinuclear complexes having X = O2CCH3 (9), O2CPh (10), I (12), and SCN (15), and by acetylacetonate anion (acac) to give mononuclear [Pd(acac)(kappa(2)-2-C6F4PPh2)] (17). In solution at room temperature the four-membered k2-2-C6F4PPh2 rings open, probably by one-ended dissociation of a Pd-P bond, to give compounds of the same composition containing bridging 2-C6F4PPh2 units, e.g., [Pd-4(mu-X)(4)(mu-2C(6)F(4)PPh(2))(4)] [X = Cl (6), I (13)], [Pd-2(mu-O2CCH3)(2)(mu-2-C6F4PPh2)(2)] (11), and [Pd-2(acac)(2)(mu-2-C6F4PPh2)(2)] (18). In some cases, only half the available chelate rings open; for example, complex 15 gives [Pd(mu-SCN)(4)(mu-2-C6F4PPh2)(2)(kappa(2)-2-C6P4PPh2)(2)] (16) and complex 12, gives [(kappa(2)-2-C6F4PPh2)Pd(mu-I)(mu-2-C6F4PPh2)pd(mu-I)(mu-2-C6F4PPh2)Pd(kappa(2)-2-C6F4PPh2)] (14), in addition to 13. Ring-opening also occurs on addition of acetonitrile to 5 or 8, forming [Pd2X2(NCMe)(2)(mu-2-C6F4PPh2)(2)] [X = Cl (19), Br (20)]. Treatment of 8 with two equivalents of PPh3 forms [PdBr(kappa(2)-2-C6F4PPh2)(PPh3)] (21) as a cis-trans mixture, which reacts with more PPh3 to give trans-[PdBr(kappa C-2-C6F4PPh2)(PPh3)(2)] (23) by displacement of the Pd-P bond of the chelate ring. The bulkier ligand tricyclohexylphosphine reacts with 8 to give an analogue (22) of 21, but it does not open the chelate ring. The X-ray structures of compounds 7-11, 13-21, and 23 are reported.