Maria Carlotta Malatesta

Hydroformylation of olefins under mild conditions: Part I: the Co4−nRhn(CO)12 + x L (n = 0, 2, 4 ; x = 0 - 9) system and preformed Rh4(CO)12−xLx clusters (x = 1 – 4)

Abstract The hydroformylation of cyclohexene, 1-pentene and styrene under mild conditions (25–50 °C, 1 atm equimolar mixture of CO and H 2 ) has been investigated using as catalyst precursor either the Co 4- n Rh n (CO) 12 + x L ( n = 0, 2, 4; x = 0 – 9) system or preformed Rh 4 CO) 12− x L x ( x = 1 – 4) substituted clusters, where L is a trisubstituted phosphine or phosphite. The activity of these systems increases as a function of x , and reaches a maximum for a L/Co 4− n Rh n (CO) 12 ( n = 2, 4) molar ratio of ca . 5 – 6. A further increase in this ratio corresponds to a smooth decrease in the activity. This ratio has apparently a negligible effect on the regioselectivity in the hydroformylation of both 1-pentene and styrene. In contrast, both the activity and the regioselectivity are significantly affected by the nature of the ligand employed as cocatalyst. When working with Rh 4 (CO) 12 as well as Rh 6 (CO) 16 , and trisubstituted phosphites as ligands, infrared spectroscopy and 31 P NMR invariably show the presence of Rh 4 (CO) 9 L 3 as the most substituted rhodium carbonyl species present in solution, and there is no evidence of fragmentation of the tetranuclear cluster during the catalytic process. In contrast, when using phosphine ligands such as PPh 3 , evidence of fragmentation to Rh 2 (CO) 6 (PPh 3 ) 2 or to Rh 2 (CO) 4 (PPh 3 ) 4 species has been obtained at the higher PPh 3 /Rh 4 (CO) 12 molar ratios. Degradation of the ligand employed as cocatalyst, particularly the arylsubstituted phosphines, is observed, and this is probably at the origin of the loss of catalytic activity of some of these systems with time.

Reactions of acetylenes with noble-metal carbonyl halides: II. Insertions into the chloro—platinum bond

Abstract The reaction of dichlorodicarbonylplatinum with ROOCC≡CCOOR (R = CH 3 , C 2 H 5 ) in benzene and toluene gives carbonylchloro(1,2- trans -dicarboalkoxy-2-chloroethenyl)platinum compounds by insertion of the active acetylene molecule into the Pt Cl bond. These chelated stable square-planar vinyl derivatives react with neutral donor ligands to give simple σ-alkenyl derivatives: [Pt(CO)Cl(ROOCC C(Cl)COOR)L] (L = C 5 H 5 N, CH 3 C 5 H 4 N), [PtCl(ROOCC C(Cl)COOR)L 2 ] (L = PPh 3 , PCH 3 Ph 2 ), and [PtCl(ROOCC C(Cl)COOR)(L L)] (L L = DPE, bipy, Me 2 bipy). The anionic species [ cis -Pt(CO)X 2 (ROOCC C(Cl)COOR)]− have been isolated as PPN salts by treating the vinyl complexes with Cl−, I− or SCN−. The stereochemistry has been elucidated from spectroscopic data (IR and 1 H NMR).

Reactions of acetylenes with noble-metal carbonyl halides : I. The reaction of 3-hexyne and 2-butyne with dichlorodicarbonylplatinum

Abstract Pt(CO) 2 Cl 2 reacts in benzene, toluene or tetrahydrofuran with 3-hexyne to give carbonylplatinumbis[di-μ-chloro,chloro(tetraethylcyclobutadiene)platinum](I), bis[dichloro(tetraethylcyclopentadienone)platinum] (III), dichloro-(tetraethyl- p -benzoquinone)platinum (IV) and dichloro(tetraethylcyclobutadiene)platinum (II). This last compound is also obtained by treating I with 1 to 3 moles of triphenylphosphine or p -toluidine. p ]The structure and reactions of III are discussed; the anion exchange reaction gives the iodo-analogue, while treatment with donor ligands gives adducts of formula [(C 2 H 5 ) 4 C 4 CO]PtCl 2 L(L = triphenylphosphine, p -toluidine, benzylamine and pyridine) and [(C 2 H 5 ) 4 C 4 CO]PtCl 2 L 2 (L = benzylamine, 3-methylpyridine). p ]2-Butyne reacts with dichlorodicarbonylplatinum to give the methyl analogous of compounds I–III.

Hydroformylation of olefins under mild conditions: Part II: The Co4−nRhn(CO)12 + xPPh2H + yL (n = 2, 4) system

Abstract The hydroformylation of cyclohexene, 1-pentene and styrene under mild conditions (25 – 50 °C, 1 atm equimolar CO and H2) in toluene or benzene using the system Co4−nRhn(CO)12 + xPPh3−mHm + yL (n = 2, 4; m = 1,2; L = trisubstituted phosphine or phosphite) as catalyst precursor has been investigated. This system was designed to generate in situ clusters containing a variable number of μ-PPh3−m bridging ligands. A set of experiments, in which x and y were independently and systematically varied in the range 1 – 4, points out that the Co4−nRhn(CO)12 + xPPh2H + yL system is an active hydroformylation catalyst for x = 1 – 2 and y = 2 – 4. Furthermore, the combined addition of PPh2H and a trisubstituted ligand L to Rh4(CO)12 apparently brings about a ‘synergetic effect’ which results in hydroformylation rates of 1-pentene and styrene often greater than those observed in the absence of PPh2H. An increase of x to 3 or 4 causes a sharp drop in the catalytic activity. Accordingly, preformed Rh3(μ2-PPh2)3(CO)5 and Rh4(μ2-PPh2)4(CO)6, both in the presence or in the absence of additional trisubstituted ligands, are substantially inactive. The Co4−nRhn(CO)12 + xPPhH2 + yL system in contrast is barely active for all tested values of x and y, although an increase in the temperature brings about some activity in a few cases. Unlike 1-pentene and styrene, the catalytic hydroformylation of cyclohexene could not be induced by combined addition of PPl2H and additional trisubstituted ligand to Rh4(CO)12 in any ratio. It is therefore conceivable that the formation of clusters containing the μ2-PPh2 group could be at the origin of the previously reported deactivation of the Rh4(CO)12 + xPPh3 system in the hydroformylation of cyclohexene.

Chemistry of iridium carbonyl clusters. Synthesis and chemical characterization of the hexanuclear anions [Ir6(CO)15(CO2R)]–(R = Me or Et) and [Ir6(CO)14(CO2Me)2]2–. Crystal and molecular structure of [N(PPh3)2][Ir6(µ-CO)4(CO)11(CO2Me)]

The anions [Ir6(CO)15(CO2R)]–(R = Me or Et) and [Ir6(CO)14(CO2Me)2]2– have been prepared by reacting [Ir6(CO)16] with Na(OR) in dry alcohol under an atmosphere of carbon monoxide. The reaction of [Ir6(CO)15(CO2Me)]– with primary and secondary alcohols such as EtOH and PriOH gives rise to specific alcoholysis. The anions [Ir6(CO)15(CO2R)]–( R = Me or Et) and [Ir6(CO)14–(CO2Me)2]2– react with acids in tetrahydrofuran solution to give quantitatively [Ir6(CO)16]. The chemical and spectroscopic characterization of the hexanuclear anions is reported. Crystals of [N(PPh3)2][Ir6(CO)15(CO2Me)] are triclinic, space group P, with unit-cell dimensions a= 10.813(3), b= 16.613(3), c= 16.061(2)A, α= 97.96(1), β= 96.20(1), γ= 94.58(2)°, and Z= 2. The X-ray structure has been solved by the heavy-atom method and refined by least squares to a final conventional R of 0.033 for 5 291 independent observed reflections. The anion consists of a slightly distorted octahedron of iridium atoms with eleven terminal and four edge-bridging CO groups and a methoxycarbonyl group σ-bonded to a metal atom. The Ir–Ir bond lengths are in the range 2.703(1)–2.870(1)A, with an average value of 2.793 A. Other average bond distances are Ir–Cterminal 1.878 and C–Oterminal 1.135 A.

Reactions of acetylenes with noble-metal carbonyl halides: III. Chemical and structural studies of σ-alkenyl complexes of platinum(II)

Abstract The reaction of [Pt(CO)Cl(ROOCC C(Cl)COOR)] and of the anions [cisPt(CO)Cl2(ROOCC C(Cl)COOR)]− (R = Me or Et) with primary and secondary alcohols (MeOH, EtOH, n-PrOH, i-PrOH, allyl-OH) gives rise to specific alcoholysis of the γ-alkoxy group. The specificity is interpreted in terms of the interaction of the β-carboalkoxy group with platinum. The crystal structure of (PPN)[cis-Pt(CO)Cl2(EtOOCC C(Cl)COOPr-i)] has been solved by X-ray analysis.

Reactions of acetylenes with noble-metal carbonyl halides. Part 7. Synthesis and chemical characterization of cationic and neutral tetrasubstituted cyclobutadiene complexes of platinum(II). X-Ray structure of dichloro(η4-1,2-dimethyl-3,4-diphenylcyclobutadiene)-(triphenylphosphine)platinum(II)

cis-[Pt(CO)2Cl2] reacts at 20 °C with 1-phenylpropyne, in non-polar solvents, to give ionic species of the type [Pt2(C4Me2Ph2)2Cl3][Pt(CO)Cl3](1) with the methyl groups of the η4-cyclobutadiene ring in a cis configuration. Analytical and spectroscopic data of complex (1) show that the cation is a dimeric platinum(II) complex with three bridging chlorine atoms; each platinum is also co-ordinated to a tetrasubstituted cyclobutadiene ring. Complex (1) is easily transformed into the corresponding neutral tetrasubstituted-cyclobutadiene derivative [Pt2(C4Me2Ph2)2Cl4](2). Complex (2) reacts with triphenylphosphine to give the monomeric derivative [Pt(C4Me2Ph2)(PPh3)Cl2](5a). Evidence for the formation of the isomer with trans methyl groups for reactions under different conditions is reported; organic by-products, obtained by dimerisation of acetylenes with CO insertion, and hexasubstituted benzene have been isolated. The crystal structure of complex (5a) has been solved by Patterson and Fourier methods from counter data and refined by diagonal least squares to a final conventional R of 0.046 for 4 358 independent observed reflections. Crystals of (5a) are monoclinic, space group P21/c, with unit-cell dimensions a= 10.900(4), b= 23.437(6), c= 13.289(4)A, β= 113.5(5)°, and Z= 4. The crystals contain discrete molecules in which the co-ordination around the Pt atom is distorted tetrahedral. Selected bond lengths (A) are: Pt–Cl(1) 2.425(3), Pt–Cl(2) 2.430(2), Pt–P 2.353(2). The cyclobutadiene ring is asymmetrically co-ordinated to platinum [Pt–C distances in the range 2.116(9)–2.214(8)A]; the C–C bond distances in the ring, which is planar, are equal to within the estimated standard deviations [av. 1.47(1)A].

Reactions of acetylenes with noble-metal carbonyl halides. Part 6. Carbonyl insertion to give cyclic organo-carbene complexes of platinum(II): synthesis and X-ray structure of the complex cis-[Pt{CC(CO2Et)C(Ph)C(CO2Et)C(Ph)O}(PPh3)Cl2]

The complex [Pt(CO)2Cl2] reacts with ethyl phenylpropiolate, PhCCCO2Et, to give [Pt{[graphic omitted]}(CO)Cl][Pt(CO)Cl3](1) which contains a six-membered carbenoid ring bonded to platinum. In acetonitrile, complex (1) gives cis-[Pt{[graphic omitted]}(CO)Cl2](2). The interconversion of complexes (1) and (2) with KCl and [Pt(CO)2Cl2] respectively are reported and a mechanism for the formation of (1) is proposed. Reaction of complex (1) with PPh3results in displacement of CO to give cis-[Pt{[graphic omitted]}(PPh3)Cl2](3). 13C N.m.r. studies of complexes (2) and (3) with specific isotopic labelling are reported. The crystal structure of complex (3) has been solved by Patterson and Fourier methods from counter data and refined by block-matrix least squares to a final conventional R of 0.048 for 5 842 independent observed reflections. Crystals of (3) are triclinic, space group P, with unit-cell dimensions a= 11.523(3), b= 11.994(4), c= 14.512(6)A, α= 106.2(1), β= 88.8(1), γ= 73.7(2)°, and Z= 2. The crystals contain discrete molecules in which the co-ordination of the platinum atom is slightly distorted square planar. Selected bond lengths (A) are Pt–P 2.244(2), Pt–C 1.933(8), Pt–Cl (trans to carbenoid carbon atom) 2.350(3), and Pt–Cl (trans to PPh3) 2.347(2). On the basis of reactivities and spectroscopic data, an unambiguous relationship has been established between compound (3) and its precursors.

Neutral substituted carbonyl clusters of iridium. Synthesis and X-ray characterization of tri-μ3-carbonyl-μ-carbonylheptacarbonylpentakis(trimethylphosphite)-octahedro-hexairidium

Abstract The reaction of Ir 6 (CO) 16 with P(OMe) 3 in toluene yields Ir 6 (CO) 11 [P(OMe) 3 ] 5 which has been shown by X-ray diffraction to contain an octahedral cluster of iridium atoms bearing five terminal trimethylphosphite ligands, three face-bridging, one edge-bridging and seven terminal carbonyl groups.

Mixed Ruthenium–Iridium Carbonyl Cluster Complexes. Synthesis of the Anions [Ru3Ir2(CO)14]2− and [Ru3Ir2(CO)14H]− and Crystal Structures of Their [tetraphenylphosphonium]+ Salts

The reaction of Ru3(CO)12 and [Ir(CO)4]- (as [PPh4]+ or [N(PPh3)2]+ salts) yields the anion [Ru3Ir2(CO)14]2- (1) which has been found to derive from the intermediate [Ru3Ir(CO)13]- anion. Treatment of (1) with acids gives the conjugated hydrido species [Ru3Ir2(CO)14H]- (2). The two anions were characterized by single-crystal X-ray diffraction of their [PPh4]+ salts. [PPh4]2[Ru3Ir2(CO)14]: space group C2/c, Z=4, a=22.121(5) Å, b=10.546(5) Å, c=25.931(5) Å, β=103.870(5)°, R=0.052 and Rw=0.130 for 3128 independent reflections with I>2σ(I ). [PPh4][Ru3Ir2(CO)14H]: space group P21/c, Z=8, a=22.833(5) Å, b=13.893(5) Å, c=25.810(5) Å, β=92.650(5)°, R=0.070 and Rw=0.150 for 12141 independent reflections with I>2σ(I). Both anions 1 and 2 have a trigonal bipyramidal metal frame. There are two independent anions in the asymmetric unit of 2 differing in their ligand stereochemistry.