OXIDATIVE-ADDITION REACTIONS INVOLVING THE MIXED-VALENCE COMPLEX [RHRE(CO)4(PH2PCH2PPH2)2] - INFLUENCE OF THE COORDINATIVELY UNSATURATED RH(+I) CENTER ON THE SATURATED RE(-I) CENTER

The mixed-metal complex [RhRe(CO)4(dppm)2] (1) (dppm = Ph2PCH2PPh2) undergoes facile oxidative-addition reactions with H2, Cl2, and HCl and also reacts with HBF4-Et2O and with the activated alkynes, dimethyl acetylenedicarboxylate (DMA), and hexafluoro-2-butyne (HFB). In the protonation reaction and the alkyne reactions these groups bridge the metals with retention of all carbonyl groups. In the reactions with H2, Cl2, and HCl both atoms of the attacking substrate bridge the metals on opposite sides of the RhReP4plane, and loss of one carbonyl group from Re occurs. Loss of one carbonyl from Re can also occur for the alkyne complexes, and this is accompanied by donation of a pair of electrons from Rh. The structure of the protonated complex [RhRe(CO)4(M-H)(dppm)2][BF4]·H2O (2) has been determined crystallographically. This compound crystallizes in the monoclinic space group P21/n with a = 17.257 (3) Å, b = 12.235 (2) Å, c = 26.354 (3) Å, β = 102.31 (1)°, V= 5436 (3) Å3, and 2 = 4. On the basis of 5535 unique observations and 388 parameters varied, the structure has refined to R = 0.043 and Rw= 0.060. Protonation at the Rh-Re bond has resulted in a lengthening of this separation from 2.7919 (6) to 3.0036 (7) Å, and a rearrangement of the carbonyl groups on Re, from a trigonal arrangement in 1 to an arrangement in which they occupy three meridional sites of an octahedron in 2. © 1990, American Chemical Society. All rights reserved.