Racemic dirhodium(II) complexes derived from orthometalated aryl phosphines, Rh 2 (O 2 -CCH 3 ) 2 (pc) 2 (pc ) orthometalated phosphine, with head-to-tail arrangement) (1-7), are isolated as pure enantiomers by conventional resolution methods. They are the first examples of dirhodium(II) chiral catalysts without chiral ligands. These compounds have been used in the cyclization of R-diazo ketones; the influence of catalyst and substrate on enantioselectivity is studied. Results are compared with those obtained for reactions catalyzed by Rh 2 (protos) 4 and Rh 2 (protos) 2 (pc) 2 [ProtosH (8) ) N-(4-methylphenylsulfonyl-L-proline] (9-22). Only catalysts 1-7 afford a high level of enantioselectivity in the synthesis of carbocycles from R-diazo ketones.

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Rh2(OOCR)2(PC)2 complexes (PC = orthometalated phosphines, OOCR = carboxylates) with very polarizable ligands, such as aromatic rings directly joined to the rhodium atoms, control chemoselectivity in competitive metal carbene transformations of α-diazo ketones. These catalysts have a mixed set of ligands that allows choosing among a big selection of ligands to gradually affect the electronic and steric properties of the catalyst. Their selectivity depends on the electrophilicity of the ligands and the polarizability of the metalated aromatic rings. Thus, Rh2(OOCR)2(PC)2 compounds [PC = (C6H4)P(CH3)(C6H5), (p-CH3C6H3)P(p-CH3C6H4)2, (C6H4)P(C6H5)2; R = C3F7 or CF3] exhibit an exceptional selectivity for aliphatic C−H insertion over aromatic substitution in catalytic decomposition of 1-diazo-5-methyl-3-phenyl-2-hexanone. Results obtained from these complexes in competitive intramolecular cyclopropanation versus tertiary C−H insertion, cyclopropanation versus aromatic substitution, and C−H insertion versus aromatic substitution are compared with those obtained for other rhodium(II) compounds, such as rhodium(II) caprolactamate (Rh2(cap)4), rhodium(II) perfluorobutyrate, and rhodium(II) acetate.

The synthesis and crystal structure of a tetranuclear palladium cluster, [Pd(PC)Br]4 (PC) = [P(C6H4)Ph2]-), is described. Cleavage of this cluster with phosphines yields the mononuclear species Pd(PC)Br(P) in the form of cis and trans isomers. An equilibrium between mono- and tetranuclear species is observed for P = PCBr.

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The reaction of compounds [ R h 2 ( O 2 C M e ) ( ~-O 2 C M e ) 2 { ~-( ~~6 ~3 ) P ( ~~~4 ~-p ) 2 } { ~( ~6 ~4 ~' -~) 3 } ] (X = H, X' = H or Me; X = Me, X' = H or Me), having a metallated and an equatorial phosphine in a head-to-tail cisoid configuration, to produce the corresponding doubly metallated compounds [Rh2(p-02CMe)2- (p-(XC,H,)P(C,H4X-p)2}2], has been studied in detail. The thermal, acid-, and base-assisted conditions include toluene solution. neat acetic acid, and different bases [PPh,, P(C6H4Me-p), or pyridine] in toluene solution and as a function of temperature, pressure and base concentration (when applicable). The doubly metallated compounds always show retention of the head-to-tail cisoid configuration according to 'P NMR spectroscopy. The reported activation parameters allow a clear differentiation between the spontaneous, acid-assisted and base-assisted processes, some of which had been previously studied (AH* = 80 k 5,68 k 1, 38 k 3 kJ mol-'; AS* = -105 2 15, -85 k 3, -150 2 30 J K-' mol-'; A P = -22.7 k 0.2, -15.3 f. 0.2, -35.0 k 0.5 cm3 mol-respectively, for the compound with X, X' = H). For the reactions under baseassisted conditions, when long reaction times and/or high added Lewis-base concentrations were applied, the non-metallated phosphine was displaced from equatorial to axial co-ordination. Under these conditions a

Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4 - x [PC] x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.

Diphenyl(3-methyl-2-indolyl)phosphine (C(9)H(8)NPPh(2), 1) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N-bridging coordination mode. On treating 1 with [Pd(O(2)CCH(3))(2)], the new complexes [Pd(mu-C(9)H(7)NPPh(2))(NCCH(3))](2) (2) or [Pd(mu-C(9)H(7)NPPh(2))(mu-O(2)CCH(3))](2) (3) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(mu-C(9)H(7)NPPh(2))(3)(mu-O(2)CCH(3))] (4), in which the bimetallic unit is bonded by three C(9)H(7)NPPh(2)(-) moieties and one carboxylate group. Using this methodology, [Pd(2)(mu-C(6)H(4)PPh(2))(2)(mu-C(9)H(7)NPPh(2))(mu-O(2)CCX(3))] (X=H (7); X=F (8)) were synthesised from the ortho-metalated compounds [Pd(C(6)H(4)PPh(2))(mu-O(2)CCX(3))](2) (X=H (5); X=F (6)). Complexes 3, 4, 7, and 8 have been found to be active in the catalytic beta-boration of alpha,beta-unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive beta-boration/cross-coupling reaction with dimethyl acrylamide as the substrate (99% conversion, 89% isolated yield).