The mixed-metal complex, [RhOs(CO)(4)(dppm)(2)][BF(4)] (1; dppm = micro-Ph(2)PCH(2)PPh(2)) reacts with diazomethane to yield a number of products resulting from methylene incorporation into the bimetallic core. At -80 degrees C the reaction between 1 and CH(2)N(2) yields the methylene-bridged [RhOs(CO)(3)(micro-CH(2))(micro-CO)(dppm)(2)][BF(4)] (2), which reacts further at ambient temperature to give the allyl methyl species, [RhOs(eta(1)-C(3)H(5))(CH(3))(CO)(3)(dppm)(2)][BF(4)] (4). At intermediate temperatures compounds 1 and 2 react with diazomethane to yield the butanediyl complex [RhOs(C(4)H(8))(CO)(3)(dppm)(2)][BF(4)] (3) by the incorporation and coupling of four methylene units. Compound 2 is proposed to be an intermediate in the formation of 3 and 4 from 1 and on the basis of labeling studies a mechanism has been proposed in which sequential insertions of diazomethane-generated methylene fragments into the Rh-C bond of bridging hydrocarbyl fragments occur. Reaction of the tricarbonyl species, [RhOs(CO)(3)(micro-CH(2))(dppm)(2)][BF(4)] with diazomethane over a range of temperatures generates the ethylene complex [RhOs(eta(2)-C(2)H(4))(CO)(3)(dppm)(2)][BF(4)] (7a), but no further incorporation of methylene groups is observed. This observation suggests that carbonyl loss in the formation of the above allyl and butanediyl species only occurs after incorporation of the third methylene fragment. Attempts to generate C(2)-bridged species by the reaction of 1 with ethylene gave no reaction, however, in the presence of trimethylamine oxide the ethylene adducts [RhOs(eta(2)-C(2)H(4))(CO)(3)(dppm)(2)][BF(4)] (7b; an isomer of 7a) and [RhOs(eta(2)-C(2)H(4))(2)(CO)(2)(dppm)(2)][BF(4)] (8) were obtained. The relationship of the above products to the selective coupling of methylene groups, and the roles of the different metals are discussed.

The growing number of late-transition-metal olefin polymerization catalysts is almost exclusively based on "hard" nitrogen or oxygen donor ligands, 1 and despite the central role of diphosphine ligands in many other areas of homogeneous catalysis, "softer" phosphine donors generally yield very poor catalysts for this application. 2 We recently reported that the fourmembered nickel(II) chelates derived from the aminodiphosphines 1a-c (Figure 1) are very efficient catalysts for polymerization of ethylene, giving high-molecularweight linear polymer. 3 Here we show that ligands 1a-c are not unique, that other diphosphines give active polyethylene catalysts when suitably activated, and that catalytic activity and polymer structure are acutely sensitive to the nature of the ligand backbone and the substituents on the phosphorus. Nickel complexes of the bis(diarylphosphino)methane ligands 2a-d were activated and screened for polyethylene catalysis under the same conditions that

The synthesis, fluxionality and reactivity of the heterobimetallic complex [FeRu(CO)2(mu-CO)2(eta-C5H5)(eta-C5Me5)] are described. Complex exhibits enhanced photolytic reactivity towards alkynes compared to its homometallic analogues, forming the dimetallacyclopentenone complexes [FeRu(CO)(mu-CO){mu-eta]1:eta3-C(O)CR"CR'}eta]-C5H5)(eta-C5Me5)]( R'= R"= H; R'= R"= CO2Me; R'= H, R"= CMe2OH). Prolonged photolysis with diphenylethyne gives the dimetallatetrahedrane complex [FeRu(mu-CO)(mu-eta2:eta2-CPhCPh)(eta-C5H5)(eta-C5Me5)], which contains the first iron-ruthenium double bond. Complexes containing a number of organic fragments can be synthesised using , and . Heating a solution of gave the alkenylidene complex [FeRu(CO)2(mu-CO){mu-eta]1:eta2-C=C(CO2Me)2}(eta-C5H5)(eta-C5Me5)] through an unusual methylcarboxylate migration. Protonation and then addition of hydride to gives the ethylidene complex [FeRu(CO)2(mu-CO)(mu-CHCH3)(eta-C5H5)(eta-C5Me5)] via the ionic vinyl species [FeRu(CO)2(mu-CO)(mu-eta]1:eta2-CH=CH2)(eta-C5H5)(eta-C5Me5)][BF4]. Compound exhibits cis/trans isomerisation at room temperature. Protonation of dimetallacyclopentenone complexes gives the allenyl species [FeRu(CO)2(mu-CO)(mu-eta1:eta2-CH=C=CMe2)(eta-C5H5)(eta-C5Me5)][BF4]. Compound exist as three isomers, two cis and one trans. The two cis isomers are shown to be interconverting by sigma-pi isomerisation. The solid state structures of these compounds were established by X-ray crystallography and are discussed.

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Reaction of [RuCo(CO)3(μ-CO)(η-C5Me5){μ-η2:η2-C(CF3)C(CF3)}] (3) with alkenes gave the bis(vinyl) complexes [RuCo(CO)3(η-C5Me5){μ-η1:η2-C(CF3)CH(CF3)}(μ-η1:η2-CHCRH)] (4a, R = H; 4b, R = Me; 4c, R = CO2Me), through loss of carbon monoxide and via regiospecific alkene carbon−hydrogen bond activation. Low-temperature 13C{1H}, 1H, and 2D NMR spectroscopic studies of the reaction of 3 with ethene suggest the reaction proceeds via several coordinated ethene intermediates and a dimetallacyclic intermediate. Reaction of 3 with 1,1-dimethylallene resulted in carbon−carbon bond formation between the allene and alkyne, giving [RuCo(CO)3(η-C5Me5){μ-η2:η4-C(CF3)C(CF3)C(CMe2)(CH2)}] (5). The structures of [RuCo(CO)3(η-C5Me5){μ-η1:η2-C(CF3)CH(CF3)}(μ-η1:η2-CHCH2)] (4a), [RuCo(CO)3(η-C5Me5){μ-η1:η2-C(CF3)CH(CF3)}{μ-η1:η2-CHCH(CH3)}] (4b), and [RuCo(CO)3(η-C5Me5){μ-η2:η4-C(CF3)C(CF3)C(CMe2)(CH2)}] (5) have been determined by X-ray crystallographic studies.