ANOMALOUS CARBONYLATION OF [PD(DPPM)(O2CCF3)]2 TO GIVE AN ASYMMETRIC MU-CO COMPLEX

The reactive palladium dimer, [Pd(dppm)(O2CCF3)]2, is carbonylated to [Pd(dppm)(O2CCF3)]2(mu-CO) in a reversible reaction with K = c. 7.2(2) x 10(4) atm-1 (P1/2 = c. 2.4 Torr). This is significantly larger than is expected based on the lambda-max = 280 nm in the electronic spectrum. The product can be isolated in analytically pure form by crystallization under a CO atmosphere. It forms crystals in the monoclinic space group Cc with a = 18.584(5), b = 28.65(1), c = 11.164(3) angstrom and beta = 95.16(2)-degrees. The structure is significantly distorted. The bonding about the two palladium atoms is quite asymmetric. While one is close to a square planar geometry with a Pd-C(O) distance of 1.90(2) angstrom, the other is significantly pyramidalized and has a longer (2.00(2) angstrom) bond to the bridging CO. The Pd-Pd distance is only 2.896(2) angstrom, much shorter than that usually observed for formally non-bonded Pd atoms.