Alberto Scrivanti

Metals in organic syntheses: XIV. NMR, IR, and reactivity studies on the olefin hydroformylation catalyzed by Pt-Sn complexes☆

Abstract Among the several hydrides formed when trans-[PtHClL2] (L = PPh3) reacts with Sncl2, only trans-[PtH(SnCl3)L2] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl3)L2]. At −10°C, cis-[PtEt(SnCl3)L2] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable. At −50°C, a mixture of trans-[PtHClL2] and trans[PtH(SnCl3)L2] reacts with ethylene to give cis-[PtEtClL2] and cis-[PtEt(SnCl3)L2] and this has been attributed to the catalytic activity of SnCl2 which dissociates from cis-[PtEt(SnCl3)L2] at this temperature. Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl3)L2], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L2]+ SnCl3−. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L2], trans-[Pt(SnCl3)(COEt)L2], trans-[PtCl(COEt)l2 · SnCl2], and trans-[Pt(COEt)(CO)L2]+ SnCl3−. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL2] with SnCl2. Trans-[PtH(SnCl3)L2] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl3)(CO)2L2], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl3)L2] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl3)L2] is allowed to react with CO. The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.

Platinum(II) trichlorostannate chemistry. On the importance of the Pt-Sn linkage in hydroformylation chemistry and a novel PtC(OSnCl2)R-carbene

Summary The reaction of trans -PtCl(COR)(PPh 3 ) 2 ( 1 ) (R = a , C 6 H 5 ; b , C 6 H 4 - p -NO 2 ; c C 6 H 4 - p -CH 3 ; d , C 6 H 4 - p -OCH 3 ; e , CH 3 , f , Et; g , Pr n ; h , Hex n ; i , CH 2 CH 2 Ph; j , Bu t ) with SnCl 2 and SnCl 2 plus H 2 are described. The reactions with SnCl 2 alone afford a mixture of trans -Pt(SnCl 3 )(PPh 3 ) 2 ( 2 ), and trans -PtCl(C(OSnCl 2 )-R)(PPh 3 ) 2 ( 3 ) with 3 having tin oxygen bond. For 1f, 1h and 1j , reactions with SnCl 2 plus H 2 give aldehydes and platinum(II) hydride complexes, whereas for 1b and 1d , no aldehydes are obtained. The significance of these results in relation to H 2 activation in the hydroformylation reaction is discussed. 31 P, 119 Sn, 195 Pt and, in a few cases, 13 C NMR data are presented.

Protonation and methylation reactions of 2-pyridyl-palladium(II) and -platinum(II) complexes

The reactions of strong acids HX and HClO4 with the 2-pyridyl complexes [PdX(μ-C5H4N-C2,N)(PPh3)]2 (X = Cl, Br), trans-[PdCl(C5H4N-C2)(PEt3)2] and [PdCl(C5H4N-C2)(dppe)] yield the N-protonated derivatives cis-[PdX2-(C5H5N-C2)(PPh3)], trans-[PdCl(C5H5N-C2)(PEt3)2]ClO4 and [PdCl-(C5H5N-C2)(dppe)]ClO4, respectively. The terminal 2-pyridyl group of trans-[PdCl(C5H4N-C2)(PEt3)2] and [PdCl(C5H4N-C2)(dppe)] also reacts with Me2SO4/NaClO4 to give trans-[PdClC5H4(l-Me)N-C2(PEt3)2]ClO4 and [PdClC5H4(l-Me)N-C2(dppe)]ClO4. Analogous N-protonation or N-methylation reactions occur with trans-[PtBr(C5H4N-C2)(L)2] (L = PEt3, PPh3). The complexes trans-[MX(C5H5N-C2)(PMe2Ph)2]ClO4 (M = Pd, X = Cl and Br; M = Pt, X = Br) exhibit restricted rotation of the protonated 2-pyridyl group around the MC bond. This and other chemical results and spectral data, such as the 13C NMR data of the PEt3 derivatives, are interpreted in terms of a significant contribution of a carbene-like limiting structure to the electronic configuration of this new type of ligand.

On the mechanism of platinum(II)/SnCl2 catalyzed hydroformylation of olefins. Studies of the reactivity of alkyl complexes containing chelating diphosphines

The complexes cis-PtCl(C2H5)(diphosphine) (diphosphine = 1,3-bis(diphenylphosphino)propane and 1,4-bis(diphenylphosphino)butane) have been used as model compounds for the hydroformylation of olefin catalyzed by the system PtCl2/diphosphine/SnCl2. They react with SnCl2 to yield the corresponding trichlorostannate complexes cis-Pt(SnCl3)(C2H5)(diphosphine), which in the absence of free ethylene decompose to form the dichloro species cis-PtCl2(diphosphine) via an unstable hydrido species. Both the chloro- and trichlorostannate-alkyl complexes react with CO to give the acyl species cis-PtX(COC2H5)(diphosphine) (X = Cl or SnCl3). When the diphosphine is 1,4-bis(diphenylphosphino)butane, oligomeric acyl complexes of trans geometry are formed. Preliminary studies of the reactivity of the acyl complexes with molecular hydrogen show that only the complexes bearing the Pt—SnCl3 moiety react at ambient conditions giving propanal as the only observed organic product.

Chemistry of tetrairidium carbonyl clusters. Part 1. Synthesis, chemical characterization, and nuclear magnetic resonance study of mono- and di-substituted phosphine derivatives. X-Ray crystal structure determination of the diaxial isomer of [Ir4(CO)7(µ-CO)3(Me2PCH2CH2PMe2)]

The reactions of the anionic cluster [NEt4][Ir4(CO)11Br] with uni- and bi-dentate phosphines and arsines have been investigated. The bromide ligand is quantitatively displaced by 1 mol equivalent of phosphine or arsine at low temperature, the only complexes being formed under these mild conditions being the monosubstituted products [Ir4(CO)11L](L = PPh3, PPh2Me, PPhMe2, or AsPh3), [Ir4(CO)11(L–L)](L–L =trans-Ph2PCHCHPPh2), and [(OC)11Ir4(L–L)Ir4(CO)11][L–L =trans-Ph2PCHCHPPh2 or Ph2P(CH2)nPPh2(n= 3 or 4)]. Similar reactions with higher than stoicheiometric amounts of phosphine (L = PPh3, PPh2Me, or PPhMe2) or diphosphine [L–L = Ph2P(CH2)nPPh2(n= 1–4), Me2P(CH2)2PMe2, cis-Ph2PCHCHPPh2, or o-Ph2PCH2C6H4CH2PPh2] give in good yields the disubstituted compounds [Ir4(CO)10(L–L)] respectively. The stereochemical arrangements of the phosphine ligands and the dynamic processes occurring in solutions of these complexes are discussed on the basis of i.r. and n.m.r, data. The structure of the diaxial isomer of [Ir4(CO)7(µ-CO)3(Me2PCH2CH2PMe2)] has been determined by X-ray diffraction. The complex crystallizes in the monoclinic space group P21/c, with cell constants a= 15.694(2), b= 10.403(2), c= 15.706(2)A, β= 92.63(2)°, and Z= 4. The structure has been solved from 2 289 diffraction intensities collected by counter methods, and refined by least-squares calculations to R= 0.087 (R′= 0.091). The four iridium atoms define a tetrahedron with three bridging CO ligands around a triangular face. All remaining carbonyls are terminally bonded and the two P atoms of the Me2PCH2CH2PMe2 ligand are found in axial positions, generating a six-membered ring.

Iminophosphine - palladium(0) complexes as catalysts for the Stille reaction

The cross-coupling of iodobenzene with tributylphenylethynylstannane or tributylvinylstannane is efficiently catalysed by iminophosphine–palladium(0)–olefin complexes of the type [Pd(η2-dmf)(P-N)] (dmf, dimethylfumarate; P-N, 1-(PPh2)-C6H4-2-CNR (R=alkyl, aryl)). The catalytic activity depends on the R substituent of the imino group: the highest reaction rates are obtained using aryl-substituted iminophosphines. Equivalent catalytic systems can be obtained using a palladium source such as Pd(OAc)2 or Pd(dba)2 (dibenzylideneacetone, dba) in combination with the iminophosphine ligands. In the coupling of iodobenzene with tributylphenylethynylstannane, the highest reaction rates are obtained using an iminophosphine/palladium molar ratio of 2:1, while in the vinylstannane–iodobenzene coupling the best P-N/Pd ratio is 1:1.

Iminophosphine-palladium(0) complexes as catalysts in the alkoxycarbonylation of terminal alkynes

Abstract In the presence of methanesulfonic acid, the palladium(0)-olefin complexes: [Pd(η 2 -ol)(P N)] [ol=dimethyl fumarate or fumaronitrile, P N=1-(Ph 2 P)C 6 H 4 -2-CH NR (R=CMe 3 or C 6 H 4 OMe-4)] catalyse the alkoxycarbonylation of terminal alkynes. Moderately good rates are obtained when the catalysts are promoted with two equivalents of the free P N ligand and a large excess of acid at 120°C. The catalytic data suggest that derivatives of the type [Pd(alkyne)(P N) n ] ( n =2–3) are the active catalytic species.

Carbonylation of terminal alkynes catalysed by Pd complexes in combination with tri(2-furyl)phosphine and methanesulfonic acid

Pd(OAc)2 in combination with tri(2-furyl)phosphine and methanesulfonic acid is an efficient catalyst for the alkoxycarbonylation of 1-alkynes. Fairly good reaction rates are obtained under mild conditions (50–80°C and P(CO)=20 bar) with high regioselectivity (ca. 95%) towards the formation of 2-substituted acrylic ester.

Synthesis and stereochemistry of mono- and di-olefin derivatives of tetrairidium carbonyl clusters

Abstract The reactions of NEt 4 [Ir 4 (CO) 11 Br] (I) with ethylene, cyclopropene, 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene and bicyclo[2.2.1]hept-2-ene in the presence of AgBF 4 gave high yields of Ir 4 (CO) 11 (olefin) (II-V), in which the olefin is bonded in an axial position on a basal Ir atom. The mono-olefin in II-V is quantitatively displaced by CO giving Ir 4 (CO) 12 or by SO 2 giving Ir 4 (CO) 11 (SO 2 ). The reaction of I with bicyclo[2.2.1]hepta-2,5-diene, cycloocta-1,5-diene or cyclooctatetraene in the presence of AgBF 4 gave Ir 4 (CO) 10 (η 4 -polyolefin), the first substitution taking place preferentially at an axial site giving Ir 4 (CO) 11 (η 2 -polyolefin), followed by chelation on a radial site of the same metal center. All the above clusters are fluxional at room temperature.

Esters and N,N-dialkylamides of 2-(trifluoromethyl)acrylic acid (TFMAA) through Pd-catalysed carbonylation of fluorinated unsaturated substrates

Abstract Esters and amides of 2-(trifluoromethyl)acrylic acid (TFMAA) have been synthesised by two different routes involving CO-chemistry. The alkoxycarbonylation of 2-bromo-3,3,3-trifluoropropene was carried out in the presence of PdCl 2 (PPh 3 ) 2 . High substrate conversions were obtained, but the yield in acrylic esters was generally low because the desired unsaturated esters reacted further adding a molecule of alcohol to the C–C double bond. The carbonylation of 2-bromo-3,3,3-trifluoropropene in the presence of secondary amines produced the corresponding unsaturated amides in high yields; the addition of the amine to the C–C double bond also occurred, but this side reaction was minimised by using secondary cyclic amines such as morpholine or piperidine. Alternatively, the acrylic esters can be obtained by hydromethoxycarbonylation of 3,3,3-trifluoropropyne using the catalytic system Pd(OCOCH 3 ) 2 /2-pyridyldiphenylphosphine/CH 3 SO 3 H. In this process the most important side product is the isomeric crotonic ester. The regioselectivity of the reaction can be controlled to a great extent by a suitable choice of the solvent.