Stephen A. Fieldhouse

Paramagnetic transition metal carbonyls : IV. ESR study of anions derived from (CO)5MnPbPh3 and (CO)4CoPbPh3 by high energy radiation

Abstract Exposure of (CO) 5 MnPbPh 3 to 60 Co γ-ray at 77 K gave one major paramagnetic species detectable by ESR spectroscopy. This exhibited an anisotropic hyperfine interaction with 55 Mn, near free-spin g -values, and a small, almost isotropic coupling to 207 Pb. The form of the A ( 55 Mn) and g -tensor components suggest an orbital of d z 2 symmetry on manganese for the unpaired electron, but this cannot be directed along the MnPb bond since the 207 Pb hyperfine coupling indicates a very low spin-density on lead. We suggest that the centre is formed by electron addition to manganese to give a formal d 7 centre, with concomitant loss of one equatorial carbonyl ligand. We defind z as the direction of the lost ligand. A second centre, detected at high gain, having a large hyperfine coupling to 207 Pb and a 31 G coupling to 55 Mn is tentatively identified as the parent cation. In marked contrast, the molecule (CO) 4 CoPbPh 3 gave a single centre having comparable 59 Co hyperfine and g -tensor components, but also a very large hyperfine coupling to 207 Pb (ca. 3300 G). Thus, in this case, an electron gain centre ( d 9 ) has been formed, the electron being accomodated in the highest MO having a large d z 2 component on cobalt ( z being now the CoPb direction). Reasons for the adoption of these different structures are discussed.

The radicals Ph4 Ás and Me4Śn

Abstract ESR spectra obtained from γ-irradiated tetraphenylarsonium salts and tetramethylstannane are shown to be in agreement with expectation for the electron-excess centres Ph 4 Ās and Me 4 Śn − .

Unstable intermediates. Part CXLVII. Electron spin resonance spectra of radicals in irradiated organotin compounds: the radicals R3Sn, R4Sn–, R5Sn, R3SnCl–, Ph6Sn2–, H2ĊSn(Me)2SnMe3, and H2ĊSn(Me)2Cl

Exposure of the following compounds or their solutions to 60Co γ-rays at 77 K gave e.s.r. spectra which are interpreted in terms of the radicals in parentheses: Me4Sn (Me3Sṅ, Me4Sṅ–, Me5Sn, H2ĊSnMe3); Et4Sn (Et3Sṅ, MeĊHSnEt3, H2ĊCH2SnEt3); Bu4Sn (Bu3Sṅ, EtĊHCH2SnBu3, RĊHSnBu3); Me3SṅCl (Me3SṅSCl–, Me3SṅH2ĊSnMe2Cl); Bu3SnCl (Bu3Sṅ, EtĊHCH2SnBu2Cl, PrĊHSnBu2Cl); Me6Sn2(Me2SṅSnMe3, H2CSnMe2-SnMe3); Ph6Sn2(Ph6Sn2–); and Ph3SnH (Ph3Sn·). Interesting aspects of these result include the pyramidal character of R3Sṅ radicals and the low spin density on tin for Me5Sṅ, which is through to have D3h symmetry with major spin density on the axial methyl groups. The absence of hyperfine interaction from the β-Cl or β-SnMe3 groups for H2ĊSn(Me)2Cl and H2ĊSn(Me)2SnMe3 suggest that these groups lie near the nodal plan of the half-occupied 2p(carbon) orbital, In complete contrast with the preferred conformation for the corresponding carbon radicals, H2ĊCR2Cl and H2ĊCR2SnMe3.

Reaction of metal carbonyls with oxygen

It is suggested that a complex previously identified as ·Mn(CO)5 is, in fact, the peroxo complex ·O2Mn(CO)5. The analogous cobalt complex ·O2Co(CO)4 has also been identified.

Reaction mechanisms of metal–metal bonded carbonyls. Part VII. Reaction of alkynes with µ-carbonyl-µ-diphenylgermanio-bis(tricarbonylcobalt)(Co–Co)

Alkynes [C2Ph2, MeC2Ph, PhC2H, and C2(CO2Et)2] displace the bridging GePh2 group from [(OC)3[graphic omitted]o(CO)3], (I), to form the well known complexes [(OC)3[graphic omitted]o(CO)3] together with (GePh2)n(n= 4–7). The kinetics of reaction of complex (I) with diphenylacetylene in decalin have been studied over a range of temperature. The rate of reaction is first order in [Complex] and [C2Ph2] and the reaction is greatly retarded by carbon monoxide. The results are consistent with a reaction mechanism that involves initial reversible ring opening to form [(OC)3Co(µ-GePh2)Co(CO)4],† a process that is also involved in a reactions of complex (I) with carbon monoxide and triphenyl- and tributyl-phosphine. A mechanism involving intermediates with terminally co-ordinated GePh2 groups cannot be conclusively ruled out but is considered to be less probable.

Unstable intermediates. Part 165. Radicals in irradiated organolead compounds: an electron spin resonance study

Exposure of PbPh3Cl and PbBrPh3 to 60Co γ-rays at 77 K gives centres having 207Pb and 35Cl or 81Br hyperfine coupling constants consistent with expectation for the parent radical anions. The electron-loss centres are thought to be the corresponding cations, with the hole largely confined to the halogen atoms. Irradiated PbMe3Cl gives a similar anionic centre in methanolic solution, but the pure material gives largely Me˙ and PbMe2(ĊH2)Cl radicals. Irradiated PbMe4 and PbEt4 pure or in toluene at 77 K. give centres thought to be PbR3˙ radicals having g⊥≈ 2.1 and g∥≈ 1.9, and abnormally large anisotropic 207Pb hyperfine coupling constants. In addition, PbMe4 gives a centre thought to be [PbMe4]–˙ and both give R˙ and PbMe3(ĊH2) or PbEt3(ĊHMe). Irradiated Pb2Ph6 gives only one clearly defined paramagnetic centre, tentatively identified as the parent anion.

Paramagnetic transition-metal carbonyls and cyanides. Part III. Electron spin resonance studies of manganese pentacarbonyl halides after high-energy irradiation

Exposure of the manganese pentacarbonyl halides [Mn(CO)5X](X = Cl, Br or I), to 60Co γ-rays at 77 K gives an S=½ centre having a g ca. 2 and a large hyperfine coupling to 55Mn and the halogen nuclei. The results are interpreted in terms of electron addition into a σ* orbital involving mainly the metal dz2 and halide pz orbitals. A second centre having two apparent g values in the g= 6 region is also formed for all the three complexes. These again exhibit hyperfine coupling to 55M and to the halogen nuclei. Various structures are considered, and it is concluded that the most reasonable are cations formed by loss of an electron and one or more carbonyl groups with unpairing of the remaining electrons to give S=5//2.