Luigi M. Venanzi

A versatile rhodium catalyst for acetalization reactions under mild conditions

Carbonyl compds. are readily acetalized under mild conditions in the presence of catalytic amts. of Rh(III)-MeC(CH2PPh2)3 complexes. Thus cyclohexanone reacted with HOCH2CH2OH to give 84% acetal I.

The facile cyclometallation reaction of 1,3-BIS[(diphenyl-phosphino)methyl]benzene

It is shown that 1,3-bis(diphenylphosphinomethyl)benzene (PCHP) readily undergoes a cyclometallation reaction with nickel(II), palladium(II), and platinum(II) species giving products of the type [MX(PCP)] [M  Ni, Pd, and Pt; X  halide and PCP  2,6-bis(diphenylphosphinomethyl)phenyl]. Cyclometallation requires the formation of intermediates trans-[MX2(PCHP)].

31P and 195Pt NMR studies of the cluster complexes [Pt3(μ2-CO)3 (tertiary phosphine)3]

Abstract 31P and 195Pt NMR data for the triangular clusters [Pt3(μ2-CO)3(tertiary phosphine)3] tertiary phosphine = PCy3, PPri3, PPri2Ph, P(CH2Ph)Ph2, are reported. The nuclearity of the complexes in solution is readily identified via 31PNMR using the multiplicity data in the 195Pt satellites. The values 1J(195Pt, 195Pt) have been measured and fall in the range 1571–1619 Hz. It is suggested that the values 2J(195Pt, 31P) and 3J(31P, 31P) can be useful indicators for the presence of platinum—platinum bonds.

Platinum-promoted cyclization reactions of amino olefins : II. Regio- and stereoselectivity in the cyclization reactions of C-methyl substituted pent-4-enylamines

Abstract The compounds 1-, 2- and 3-methylpent-4 enylamine cyclize, in a reaction medium containing [PtCl4]2-, to the corresponding cis- and trans-dimethylpyrrolidines showing marked regio and stereoselectivity effects. The following cyclization reactions are also reported: a) that of hex-4-enylamine which gives a mixture of 2-ethylpyrrolidine and 2-methylpiperidine, b) that of 2,2-dimethylpent-4-enylamine which produces 2,4,4-trimethylpyrrolidine and c) that of 2,2-dimethylhex-4-enylamine which results in the formation of 2-ethyl-4,4-dimethylpyrrolidine and 2-methyl-5,5-dimethylpiperidine. The X-ray crystal structures of trans-[PtCl2(amine)(Et3P)] (amine = cis-2, 4-dimethylpyrrolidine and cis-2,3-dimethylpyrrolidine) are reported.

31P and 195Pt NMR studies on the clusters [Pt4(μ2-CO)5L4]. L=PEt3, PMe2Ph, PMePh2, PEt2But: the molecular structure of a monoclinic modification of [Pt4(μ2-CO)5(PMe2Ph)4]

Abstract Several clusters complexes of composition [Pt4(μ2-CO)5L4] have been synthesized and characterized, using 31P and 195Pt NMR. L = PEt3, PMe2Ph, PMePh2, PEt2But. The molecular structure of a new monoclinic modification of the PMe2Ph derivative has been determined: space group P21/n with a = 19.698(4), b = 10.9440(20), and c = 21.360(6) A, β = 112.432(18)°, Z = 4. Using 4751 reflections measured at 290 ± 1 K on a four-circle diffractometer the structure has been refined to R = 0.0846. The molecule has no imposed symmetry, but the central Pt4(CO)5P4 core has the approximate C2v architecture established for the previously known orthorhombic modification. The Pt4 unit is thus a highly distorted, edge-opened (3.3347 A) tetrahedron, with five edge-bridging carbonyl and four terminal phosphine ligands. In contrast to the crystallographic results 31P and 195Pt NMR spectra reveal equivalent 31P and 195Pt spins, which can be interpreted in terms of a tetrahedral arrangement of platinum atoms. It is suggested that this equivalence arises from time-averaging of all possible isomeric edge-opened tetrahedra.

31P and 195Pt nmr studies on the triangular cluster complexes [Pt3(μ-CO)3(tertiary phosphine)4]

Abstract 31 P and 195 Pt NMR data for the triangular clusters [Pt 3 (μ-CO) 3 L 4 ] (L = PEt 3 , PMe 2 Ph, PMePh 2 , PEt 2 Bu t , P(CH 2 Ph)Ph 2 ) are reported. The 31 P measurements show the presence of non-equivalent phosphines and the 195 Pt spectra identify two different types of platinum. There are two markedly different 1 J( 195 Pt, 195 Pt) coupling constants with ranges of 1808–1840 Hz (base to base) and 385–586 Hz (top to base), as well as different 2 J( 195 Pt, 31 P) values, 411–459 Hz and 272–292 Hz. The two 1 J( 195 Pt, 31 P) coupling constants also vary considerably and depend upon the number of coordinated phosphine ligands. These and the remaining NMR data suffice for purposes of proof of structure.

Rhodium(I) complexes of the type [Tp3R,5RRh(LL)] (LL = 2 CO, NBD, COD) with trifluoromethyl substituted tris (pyrazolyl) borate ligands and their dynamic behaviour in solution. The X-ray crystal structure of TpCF3MeRh(CO)2☆

Three seriesof Rh(I) complexes of the type Tp3R,5RRh(LL), with LL = 2 CO (1), norbornadiene (NBD) (2) and 1,5-cyclooctadiene (COD) (3) and the tris (pyrazolyl)borate (Tp) ligands 3R=5R=Me (a), 3R=CF35R=Me (b); and 3R=5R=CF3 (c) were synthesized and fully characterized by IR and multinuclear NMR spectroscopy. Three isomeric forms were identified in solutions of these complexes: two square-planar isomers with a κ2-Tp3R,5R ligand, the uncoordinated pyrazolyl ring occupying either an equatorial position (type A), or an axial position (type B), and a five-coordinate species with a κ3, Tp3R,5R ligand (type C). In the carbonyl complexes 1 the dynamic equilibria between these isomers are solvent dependent. Interestingly, solutions of complex 1c contained all three isomers simultaneously. 103Rh and 13C NMR spectral studies indicate that the NBD compounds, 2, preferentially form square-planar complexes when TpCF3,Me and TpCF3,CF3 are present, while for the COD complexes, 3, square-planar complexes are preferred for all three Tp-type ligands. The X-ray structure of TpCF3,MeRh(CO)2 (1b) was determined (spacce group C2/ c,a = 21.271(9), b = 11.004(3), c = 21.563(9) A, β = 114.93(3)°, V=4577(3) A3, Z = 8, R = 3.41, Rw = 4.70). Its structure is of type B, with the third pyrazolyl ring axially placed, the N(4) being almost directly above the Rh atom but exerting only a weak Rh-N interaction.

Some iridium(I) and iridium(III) complexes with the tripod-like ligand CH3C(CH2PPh2)3 (triphos) and the X-ray crystal structure of [IrCl(CO)(triphos)]

Abstract The compound [IrCl(CO)(triphos)] ( 1 ), has been reinvestigated and its X-ray crystal structure is reported. The crystals are orthorhombic, space group Pbca , with a 18.941(6), b 22.193(8), c 17.501(7) A, Z = 8. The structure was solved by the heavy atom method and refined by full-matrix least-squares to the conventional R factor value of 0.074 for 6462 reflections. The metal atom coordination is trigonal bipyramidal, with the three phosphorus atoms occupying one axial and two equatorial positions. The other equatorial position is occupied by CO while Cl is coordinated axially. Compound 1 readily undergoes a series of oxidative-addition reactions with H 2 , HCl and Cl 2 , giving [IrH 2 (CO)(triphos)] + ( 4 ) [IrHCl(CO)(triphos)] + ( 3 ), and [IrCl 3 (triphos)] ( 5 ), respectively. Compounds [IrH(CO)(triphos)] ( 2 ) and [IrH n Cl 3- n (triphos)] ( n = 1, 2, 3) have also been obtained from 1 and 5 , respectively, by treating them with a variety of hydride sources.

Palladium-promoted cyclization reactions of aminoalkenes

Abstract The trifluoromethanesulphonate salts of the aminoalkenes CH2CH(CH2)3-NH2, its 2-methyl, 2,2-dimethyl and N-iso-propyl-derivatives, and CH2CH-(CH2)4NH2 cyclize in the presence of [PdCl2(PhCN)2] and a nitrogen base to produce the corresponding C- or N-substituted 2-methylpyrrolidines and 2-methylpiperidine. E-CH3CHCH(CH2)3NH2 produces 2-ethylpyrrolidine and a small amount of 2-methylpiperidine. The regio-selectivity of these reactions differs from that observed for the cyclization of the same substrates promoted by [PtCl4]2-: (1) the palladium reaction with 2-methylpent-4-enylamine produces ca. a 4 : 6 ratio of cis- and trans-2, 4-dimethylpyrrolidine while with platinum the converse is true; (2) there is a more marked tendency for attack of the amine at the more substituted alkene carbon atom in the palladium than in the platinum reactions.

Acetalization and Transacetalization Reactions Catalyzed by Ruthenium, Rhodium, and Iridium Complexes with {2-{{Bis[3-(trifluoromethyl)phenyl]phosphino}methyl}-2-methylpropane- 1,3-diyl}bis[bis[3-(trifluoromethyl)phenyl]phosphine] (MeC[CH2P(m-CF3C6H4)2]3)

The complexes [RhCl(3−n)(MeCN)n(CF3triphos)](CF3SO3)n (n=1, 2; CF3triphos=MeC[CH2P(m-CF3C6H4)2]3) and [M(MeCN)3 (CF3triphos)](CF3SO3)n (M=Ru, n=2; M=Ir, n=3) are catalyst precursors for some typical acetalization and transacetalization reactions. The activity of these complexes is higher than those of the corresponding species containing the parent ligand MeC[CH2P(C6H5)2]3(Htriphos). Also the complexes [MCl3(tripod)] (tripod=Htriphos and CF3triphos) are active catalysts for the above reactions. The complex [RhCl2(MeCN)(CF3triphos)](CF3SO3) catalyzes the acetalization of benzophenone.