The thermal cis-trans isomerization of cis-transoidal polyphenylacetylene (PPA) synthesized with Noyori's catalyst [Rh(C'CPh)(norbornadiene)(PPh 3 ) 2 ] has been investigated under both ambient and inert atmospheres in solution and in bulk. In all cases, an intramolecular cyclization results in cis-trans isomerization, and subsequent chain cleavage produces 1,3,5-triphenylbenzene. This reaction is accelerated by the presence of air, particularly when the reaction takes place in solution. Decreases in the cis content and molecular weight show that the intramolecular cyclization process takes place at 23°C in solution. The mechanism of this reaction is identical to that reported previously for cis-cisoidal and cis-transoidal PPA synthesized with Ziegler-Natta catalysts.

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The present paper deals with a rational attempt to achieve the hydroformylation of diphenylacetylene onto a hydrido triruthenium cluster complex incorporating the 2-(methylamino)pyridyl group (abbreviation: MeNpy) as a hemilabile ancillary ligand [note: in all species discussed below, the bridgehead µ 2 -N atom is linked to the centers labeled as Ru(1) and Ru(2), whereas the pyridyl nitrogen is bound to Ru(3)]. The complex Ru 3 (µ-H)(µ-MeNpy)-(CO) 9 (1) is shown to react cleanly with diphenylacetylene to give the alkenyl complex Ru 3 -(µ-MeNpy)(µ-PhCdCHPh)(CO) 8 (2), the structure of which is reported. The reaction of 2 with 1 equiv of PPh 3 proceeds to completion within less than 3 min at 25 °C, giving two propenoyl complexes, namely, Ru 3 (µ-MeNpy)(µ-OdC-PhCdCHPh)(PPh 3 )(CO) 7 (3) (48% yield) and Ru 3 (µ-MeNpy)(µ-OdC-PhCdCHPh)(PPh 3 ) 2 (CO) 6 (4) (19% yield), both fully characterized by spectroscopic methods and X-ray analysis. Complex 3 is an adduct of 2 with PPh 3 . The incorporation of the phosphine has caused a migratory CO insertion of the alkenyl group. The phosphine occupies an equatorial coordination site on Ru(1), in cis position relative to the nitrogen atom of the amido bridge. The newly formed propenoyl group occupies an equatorial bridging position across the Ru(1)-Ru(3) edge, with the acyl oxygen bound to Ru(1), in cis position relative to both the bridgehead nitrogen atom and the phosphine. The molecular structure of the second propenoyl compound, Ru 3 (µ-MeNpy)(µ-OdC-PhCdCHPh)-(PPh 3 ) 2 (CO) 6 (4), is formally derived from the previous one, 3, by a simple substitution of an equatorial CO of Ru(2) by PPh 3 . The use of a 2-fold amount of phosphine for the above reaction modifies only slightly the relative abundance of 3 (30%) and 4 (44%). This indicates that 3 is not the kinetic product of the reaction between 2 and a phosphine. Further reaction of 4b with CO induces loss of one PPh 3 and incorporation of two CO ligands. This produces the open 50e cluster Ru 3 (µ-MeNpy)(µ-OdC-PhCdCHPh)(PPh 3 )(CO) 8 (5), in which the bridging propenoyl group now spans the open edge Ru(1)-Ru(2) (the remaining phosphine occupies an equatorial site cis to the acyl oxygen). Treatment of 2b with CO (1 atm, 25 °C, 20 min) also promotes migratory CO insertion, giving the 50e propenoyl complex Ru 3 (µ-MeNpy)(µ-OdC-PhCdCHPh)(CO) 9 (6b), whose structure has been determined. The propenoyl group spans the open edge Ru(1)-Ru(2). Although stable in CO-saturated solutions under CO atmosphere, the complex reverts rapidly to 2 within 30 s under inert atmosphere. Treatment of 6 with CO/H 2 gas mixtures under ambient conditions produces R-phenylcinnamaldehyde with concomitant recovery of 1, showing that the hydroformylation of diphenylacetylene can be achieved in a stepwise manner through the cyclic reaction sequence 1 f 2 f 6 f 1. Under nonoptimized catalytic conditions, the amount of R-phenylcinnamaldehyde obtained corresponds to about eight cycles. The metal-containing species recovered in the reactor through the catalytic ru...

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Reactions of the cluster complexes [PPN][Ru 3 (µ 3 -η 2 -Xpy)(CO) 9 ] (1-3) (Xpy ) 2-substituted pyridyl group; 1, X ) PhN; 2, X ) MeN; 3, X ) S) with phosphines in THF solution are described. Complex 1, containing the 2-anilinopyridyl group, reacts with P(n-Bu) 3 or PPh 3 at room temperature to yield the addition product [PPN]-(Ru 3 (µ-η 2 -PhNpy)(CO) 9 L] (4a,b) (a, L ) P(n-Bu) 3 ; b, L ) PPh 3 ). This adduct slowly loses either the phosphine or a CO ligand to give a mixture of the starting antecedent species and its monosubstituted derivative. The corresponding intermediate adducts are not seen with 2-(methylamino)pyridyl and 2-thiopyridyl complexes 2 and 3 which react with P(n-Bu) 3 to yield respectively the monosubstituted complex [PPN][Ru 3 (µ 3 -η 2 -MeNpy)(CO) 8 P-(n-Bu) 3 ] (5a) and the disubstituted complex [PPN][Ru 3 (µ 3 -η 2 -Spy)(CO) 7 (P(n-Bu) 3 ) 2 ] (6a). Kinetic results for these reactions are reported. The reactions are first-order in complex and first-order in ligand concentrations. It is proposed that the initial step for these reactions is an associative nucleophilic attack of phosphine ligands on the metal atom accompanied by opening of the µ-X bridge bond to form the adducts [PPN][Ru 3 (µ-η 2 -Xpy)-(CO) 9 L]. The rates of reaction increase in the order 2-MeNpy < 2-Spy < 2-PhNpy. The reactivity order of these complexes toward nucleophiles is discussed in terms of electronic effects of their ancillary ligands.

The compound [Ru3(mu-H)(mu3-eta2-ampy)(CO)9] (1; Hampy =2-amino-6-methylpyridine) reacts with diynes RC4R in THF at reflux temperature to give the ynenyl derivatives [Ru3(mu3-eta2-ampy)(mu-eta3-RC...CC-CHR)(mu-CO)2-(CO)6] (2: R=CH2OPh; 3: R=Ph). These products contain a 1,4-disubstituted butynen-3-yl ligand attached to two ruthenium atoms. The compound [Ru3(mu-eta2-ampy)[mu3-eta6-PhCC5(C...CPh)-HPh2](CO)7] (4), which contains an eta5-cyclopentadienyl ring and a bridging carbene fragment, has also been obtained from the reaction of 1 with diphenylbutadiyne. This compound arises from a remarkable [3+2] cycloaddition reaction of a preformed 1,4-diphenylbutynen-4-yl ligand with a triple bond of a second diphenylbutadiyne molecule. The reactivity of the ynenyl derivatives 2 and 3 with diynes and alkynes has been studied. In all cases, compounds of the general formula [Ru3(mu-eta2-ampy)[mu3-eta5-C(=CHR)C=CRCR1=CR2](CO)7] (5-17) have been obtained. They all contain a ruthenacyclopentadienyl fragment formed by coupling of the coordinated ynenyl ligand of 2 (R = CH2OPh) or 3 (R = Ph) with a triple bond of the new reagent (the CR1=CR2 fragment results from the incoming diyne or alkyne reagent). While most of the products derived from 2 have the alkenyl C=CHR fragment with a Z configuration (R cis to Ru), all the compounds obtained from 3 have this fragment with an E configuration. Except 2 and 3, all the cluster complexes described in this article have a five-electron donor ampy ligand attached to only two metal atoms, a coordination mode unprecedented in cluster chemistry.

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Dehydrogenative coupling reactions of bis(hydrosilyl)benzenes with [Ru3(CO)12] afford moderate yields of the polymers [-SiRR′-Ru(CO)4-Ru(CO)4-SiRR′-C6H4-]n which exhibit large solvent-dependent change of the UV-VIS spectra. The absorption maximum of the polymer is markedly red-shifted, compared with monomeric complex [PhMe2SiRu(CO)4Ru(CO)4SiMe2Ph].