George E. Hartwell

Application of 13C NMR to the determination of metal—carbon σ bond formation in cyclometallation reactions with nitrogen donor ligands

A series of cyclometallated complexes of the nitrogen donor ligands, azobenzene, N,N-dimethylbenzylamine, 8-methylquinoline, and benzo[h]quinoline have been examined by 13C NMR. The total number of expected aromatic quaternary and CH carbon atom resonances were determined by comparison of the noise decoupled and single frequency off resonance decoupled spectra of a given complex. In this manner it can be readily determined that cyclometallation may have occurred. In those cases where metal-13C coupling is observed an unambiguous determination of metal—carbon σ bond formation is achieved.

Preparation and Nuclear Magnetic Resonance Study of Phosphorus Compounds Containing Alkenyl Functional Groups

The phosphines PPhn(CH2CH2CH=CH2)3−n, n = 2–0, PPhn(CH2CH2CH2CH=CH2)3−n, n = 1 or 2, and PPh2CH2CH = CH2 have been synthesized and studied by 1H and 31P magnetic resonance. The n.m.r. spectra of PPh2(OCH2CH=CH2), its oxide, O=PPh2(OCH2CH=CH2), and its Arbuzov rearrangement product, O=PPh2(CH2CH=CH2), have been investigated by 31P decoupling of the proton spectrum, selective proton decoupling of the 31P spectrum, and comparison with computer-simulated spectra to determine the spin–spin coupling constants. The n.m.r. spectra of the related oxides O=PPh2CH2CH2CH=CH2, O=P(CH2CH2CH=CH2)3, and O=P(OCH2CH=CH2)3 are also assigned. The data indicate that 3JPH > 2JPH for alkenylphosphines, 2JPH is larger for phosphine oxides than for phosphines, and 3JPH is little changed in comparing phosphorus(III) with phosphorus(V) compounds.

Olefin complexes of rhodium(I) containing the ligands but-3-enyldiphenylphosphine and diphenylpent-4-enylphosphine

Abstract But-3-enyldiphenylphosphine (mbp) and diphenylpent-4-enylphosphine (mpp) react with Rh2Cl2(C2H4)4 (molar ratio 2 1 to form the four coordinate dimeric complexes Rh2Cl2(mbp)2 and Rh2Cl2(mpp)2 respectively, while but-3-enyldiphenylphosphine reacts with Rh2Cl2(C2H4)4 (molar ratio 4 1 ) to form RhCl(mbp)2, a five coordinate complex in the solid state. The dimers further react with sodium tetraphenylborate to give the π-bonded tetraphenylborate complexes Rh[mbp][C6H5)4B] and Rh[i-mpp][(C6H5)4B] where i-mpp = (C6H5)2P(CH2CH2CHCHCH3). RhCl(CO)(mbp)2 reacts with sodium tetraphenylborate to form the five coordinate cationic complex [Rh(CO)(mbp)2][(C6H5)4B]. Both RhCl(CO)(mbp)2 and RhCl(mbp)2 react with hydrogen in methanol saturating the olefin to form RhCl[CO][(C6H5)2P(C4H9)]2 and Rh2Cl2[(C6H5)2P(C4H9)]2 respectively.

Tris-olefin complexes of rhodium(I) and iridium(I) containing the tetradentate ligands tris(but-3-enyl)phosphine and tris(pent-4-enyl)phosphine☆

The rhodium(I) and iridium(I) complexes, RhX(tbp), RhX(tpp), X = Cl, Br or I, and IrCl(tbp) and IrCl(tpp) where tbp = P(CH2CH2CH=CH2)3 and tpp = P(CH2CH2CH2CHCH2)3 have been prepared. These compounds, except for RhI(tbp), all exhibit the same “umbrella” type five coordinate structure in the solid state, in which all three olefins are bonded to the metal. At −60° in solution, RhI(tbp) adopts the same five coordinate stereochemistry. Due to restricted rotation, the methylene protons in RhCl(tbp) become inequivalent at low temperature. RhCl(tbp) forms 11 adducts with carbon monoxide and triphenylphosphine. Infrared, Raman and PMR studies conclude that the metalolefin bond is stronger for the iridium complexes compared to the corresponding rhodium complexes.

Molybdenum carbonyl complexes of unsaturated tertiary phosphines

Abstract The photochemical and thermal reactions between Mo(CO) 6 , Mo(CO) 4 - norbernadiene, Mo(CO) 3 -cycloheptatriene or Mo(CO) 4 Cl 2 and the ligands Ph n P(CH 2 CH 2 CHCH 2 ) 3−n , where n = 0,1 or 2, yield a variety of complexes in which the olefin has an influence on the products that can be isolated. Although chelated products are formed, the maximum coordinating ability of each ligand is not realized during olefin replacement reactions. Species are formed that contain an increased number of carbonyls or that polymerize in preference to chelation through metal— olefin bond formation. These species are not analogous to the products obtained with saturated tertiary phosphines.

Five coordinate rhodium(I) olefin complexes containing the ligand bis(but-3-enyl)phenylphosphine

Abstract The complexes Rh2X2(bbp)2 (X = Cl, Br or I; and bbp = bis(but-3-enyl)phenylphosphine) have been prepared. These complexes have been characterized as five coordinate dimers in which the unsaturated phosphine acts as a tridentate ligand. Carbon monoxide reacts reversibly with the dimers forming the five coordinate monomeric compounds RhX(CO)(bbp). Mass spectral, infrared, Raman, and proton magnetic resonance data are consistent with the above formulations.

Crystal and molecular structure of chlorobis(3-butenyldiphenylphosphino)rhodium(I)

The structure of chlorobis(3-butenyldiphenylphosphino)rhodium(I) was determined by three-dimensional x-ray diffractometer techniques. The compound crystallizes in the space group P2/sub 1//c with cell constants of a = 10.697 (5) A, b = 9.832 (5) A, c , 36.44 (2) A, and ..beta.. = 96.42 (3)/sup 0/; Z= 4. The structure, solved by heavy-atom techniques, was refined by full-matrix least-squares methods using the 4218 reflections which had intensities 3 sigma above background to an unweighted R value of 5.1 percent. The coordination around the Rh(I) atom is best described as trigonal bipyramidal with one phosphorus and the midpoints of the two olefinic groups forming the equatorial plane which lies 0.13 A toward the Cl atom from Rh(I). In spite of the different geometric constraint imposed by the butenyl chains, both olefinic groups lie in the equatorial plane (within 8.5/sup 0/). This phenomenon and the placement of the best ..pi.. acceptor in the equatorial plane are interpreted in terms of a synergetic cooperation between the ..pi.. and sigma bonding in this plane.

Palladium(II) and platinum(II) complexes of unsaturated tertiary phosphines

Abstract A series of square planar Pd II and Pt II complexes of the type MX 2 (L) [X = Cl, Br, I and L = Ph n P(CH 2 CH 2 CHCH 2 ) 3 − n ; n = 0–2] have been prepared and studied by 1 H and 31 P magnetic resonance, and infrared and Raman spectroscopy. The strength of the metalolefin bond is found to be in the order Pt > Pd. When L = PhP(CH 2 CH 2 CHCH 2 ) 2 or P(CH 2 CH 2 CHCH 2 ) 3 , IR and Raman data indicate only one olefin is coordinated in both the solid state and solution. On the PMR timescale, the olefins undergo rapid intramolecular exchange, offering a system in which one observes average HH and PtH coupling.

Triarylstibine complexes of Rhodium(I)

Abstract The complexes that can be isolated from the reaction of R3Sb (R = Ph, o- or p-CH3C6H4) with [RhCl(CO)2]2, [RhCl(cod)]2 and Rh(acac)(CO)2 are RhClCO(R3Sb)n (n = 2 and/or 3, depending upon solvent and the size of R), RhCl(cod)(R3Sb)2 and Rh(acac)CO(R3Sb)2 respectively. Five coordination is favored in the solid state. However, there is considerable dissociation of R3Sb in solution. RhClCO(R3Sb)n (n = 2 or 3), RhCl(cod)(R3Sb)2 and RhCl(R3Sb)3 react immediately with CO to yield cis-RhCl(CO)2R3Sb.

Oxidative addition reactions of rhodium(I) complexes containing bidentate unsaturated tertiary phosphine ligands

Abstract The oxidative addition reactions of RhCpPPh 2 R (R = OCH 2 CHCH 2 (map) or CH 2 CH 2 CHCH 2 (mbp)) have been investigated. RhCp(map) and RhCp(mbp) react with one mole of X 2 (X = Br or I) to yield stable dihalide adducts with a non-coordinated olefin. RhCp(mbp) reacts with methyl halides primarily yielding ionic compounds which do not undergo migration of the methyl group to the coordinated olefin. The isolation of these ionic intermediates, [RhCp(mbp)CH 3 ]X, is consistent with formation by a S N 2 reaction mechanism with the Rh 1 complex acting as the nucleophile. The reaction of RhCp(mbp) with MeX also yields small amounts of products which contain a metallocyclic ring, RhCp[CH(CH 2 CH 3 )CH 2 CH 2 PPh 2 ]X (7%) and possibly RhCp[CH(CH 3 )CH 2 CH 2 CH 2 PPh 2 ]X (1%). RhCp(mbp) also reacts in solution with hydrogen halides, benzyl and allyl halides but not with carbon monoxide. In contrast, RhCp(map) reacts with carbon monoxide to form RhCp(map)CO but does not react with the organohalides. 1 H NMR and infrared data indicate a considerably stronger rhodiumolefin interaction for the Rh 1 than for the Rh III complexes, and this difference is related to the reactivity of the coordinated olefin. Thus, RhCp(mbp) can be recovered unreacted from a methanolic solution of sodium methoxide while the ionic Rh III complex [RhCp(mbp)CH 3 ]I, which has less electron density on the olefin, reacts with the nucleophile yielding RhCp[CH 2 CH(OCH 3 )CH 2 CH 2 PPh 2 ]CH 3 .