Colin S. Cundy

Tetrakis(triethylphosphine)nickel(0) and related complexes

The preparation, properties and some oxidative addition reactions of the trialkylphosphine complexes (Et3P)4Ni and (n-Bu3P)2Ni(1,5-C8H12) are described.

The role of the transition metal in the homogeneous catalytic polymerisation of strained organosilicon heterocycles

Abstract A number of transition metal complexes have been examined as catalysts for the polymerisation of silacyclobutanes R(X) SiCH 2 CH 2 C H2(R = X = CH3 or OCH3; or R=CH3 and X = Cl). Active complexes include (C2H4PtCl2)2, [(CO)2RhCl]2, [(C6H5)3P]3RhCl and [(C6H5)3P]3RhCH3, whereas the followin8 are relatively inactive: [(C6H5)3P]2Rh(C6H4PPh2), [(C6H5)3P]4RhH, [(C6H53P]2PtCl2, [(C6H5)3P]2Ir(CO)Cl, and [(CH3)3SiCH2]4Zr. A mechanism is suggested which involves successively: (a) insertion of the transition metal M into a SiC bond (ring expansion of the SiC3 ring by oxidative addition to the transition metal), (b) formation of a linear M-aIkyl by halogen or alkyl transfer from M to Si (ring opening), (c) propagation by repeated combination of (a) and (b) and (d) chain termination by β-hydrogen abstraction or alkane elimination Evidence is provided by product isolation and by approximate rate measurements.

Silylmethyl and related complexes : III Reaction of (trimethylsilyl)methyl, (dimethylsilyl)methyl or neopentyl alkylating reagents with chlorotris(triphenylphosphine)rhodium(I): Steric acceleration to decomposition of the presumed transition metal alkyl intermediate☆

Abstract Reaction of (Ph 3 P) 3 RhCl with Me 3 CCH 2 Li, Me 3 SiCH 2 MgCl, (Me 3 CCH 2 ) 4 Zr,(Me 3 SiCH 2 ) 4 Ti, or (Me 3 SiCH 2 ) 4 Zr gives the appropriate alkane (Me 4 C or Me 4 Si) and (Ph 3 P) 2 Rh( o -C 6 H 4 PPh 2 ) in equimolar amounts. The intermediate rhodium(I) alkyl (Ph 3 P) 3 RhR (R = Me 3 SiCH 2 , Me 3 CCH 2 ) was not isolated under conditions where the known methyl analogue (R = Me) is stable: it is inferred that the bulky alkyl groups containing noβ-hydrogen atoms facilitate the internal metallation of the phenylphosphine ligands leading to the observed products. When R = HMe 2 SiCH 2 , decomposition is predominantly via β-elimination but (Ph 3 P) 4 RhH is the isolated hydridic product.

Bonding studies of compounds of boron and the group IV elements: XI. Photoelectron spectra of strained cyclic organosilicon compounds

The He(I) photoelectron (PE) spectra of a series of silacyclobutanes XX′-SiCH2CH2CHR and of a 1,3-disilacyclobutane Me2SiCH2SiMe2CH2 are reported and analysed. The ionisation potentials (IPs) of the uppermost ring molecular orbitals (MOs) (a1 and b1 within the C2v point group) are definitively assigned on the basis of symmetry arguments, comparisons with simpler systems such as SiX4 and (CH2)n, and extended Huckel theory (EHT) calculations, and comments are made on the origin of some of the other bands. The effects on these MOs of changes in the substituents X, X′, and R are discussed; they correlate well with the assignments and calculations. The effects of transannular interactions are assessed by comparisons with the spectrum of 1,1-dimethylsilacyclopentane.

Reactions of hydridosilacyclobutanes with low-valent complexes of iron or platinum☆

Abstract Unstable transition metal compounds formed from hydridosilacyclobutanes are described: 1-methyl-1-silacyclobutane reacts with nonacarbonyldiiron to give the complexes [Fe(CO)4(H){ Si(Me)CH 2 CH 2 C H2}] and [ Fe{CH 2 CH 2 CH 2 Si (H)Me}(CO)4], and with bis(triphenylphosphine)(ethylene)platinum(0) to give [Pt(H)(PPh3)2{ Si(Me)CH 2 CH 2 C H2}].

Photochemical synthesis and electron spin resonance characterisation of stable trivalent metal alkyls (Si, Ge, Sn) and amides (Ge and Sn) of Group IV elements

The reaction of MCl2(M = Ge or Sn) or Si2Cl6 with R1Li or (R22N)Li [R1=(Me3Si)2CH, R2= Me3Si] and subsequent irradiation affords the stable metal-centred radicals R13Si·, R13M·, or (R22N)3M·(e.g. R13Ge· has t½ > 4 months in C6H6 at 20 °C), the solution e.s.r. spectra of which show well defined hyperfine splittings [e.g. for (R22N)3Ge·, a decet of septets, due to coupling with 73Ge (I= 9/2) and 14N (I= 1)].

Metal–silacyclobutane complexes. Part 1. Derivatives of iron and manganese

The complexes [M{[graphic omitted]H2}][M = Fe(η-C5H5)(CO)2, Fe(η-C5H5)(CO)(PMePh2), Fe(η-C5H5)(PMePh2)2, or Mn(CO)5] have been prepared and their reactions (substitution at Si or Fe, Fe–Si bond cleavage, or ring opening) studied. The complex [Fe(η-C5H5)(CO)2,{[graphic omitted]H2}] reacts with hydrogen chloride to give [Fe(η-C5H5)(CO)2H] and Cl(Me)[graphic omitted]H2(minor reaction) together with [Fe(η-C5H5)(CO)2{SiMe(Prn)Cl}](major product), and with Cl2 to afford [Fe(η-C5H5)(CO)2Cl] and Cl(Me)[graphic omitted]H2, methanolic K[OH] cleaves first the Fe–Si bond and then the displaced silacyclobutane ring; catalytic polymerisation gives {–Si(Me)[Fe(η-C5H5)(CO)2]CH2CH2CH2–}n. Hydrogen-1 n.m.r. and mass spectrometric data are presented.

1-[(π-Cyclopentadienyl)dicarbonyliron]-1-methylsilacyclobutane and related iron-substituted silacyclobutanes

Abstract Silicon-transition metallic silacyclobutanes CpFe(L 2 ) Si(Me)CH 2 CH 2 C H 2 [L = CO or Ph 2 MeP; or L 2 = (CO)(Ph 2 MeP)] have been prepared and their reactions (substitution at Si or Fe, Si—Fe cleavage, or ring-opening) studied.

Reactions of strained organosilicon heterocycles with nonacarbonyldi-iron(0). Part I. Reactivity and mechanism

The formation of 2,2,2,2-tetracarbonyl-1-sila-2-ferracyclopentanes by the reaction of silacyclobutanes with nonacarbonyldi-iron is described, and the nature of the process discussed. Completely regioselective reactions are found with Me2[graphic omitted](Me)H[Si–CH2 and not Si–C(Me)H cleavage] and with two silabenzocyclobutenes R2[graphic omitted]H2(R = Me or Ph)[C(arly)–Si and not C(alkyl)–Si cleavage]. With mixtures of the two isomers of XMe[graphic omitted]H2(X = Bun, isomer ratio 4:1: X = MeO, isomer ratio 7:3) the reaction is stereospecific, there being no significant change in isomer ratio between the reactant and product. It is concluded that this facile [Fe(CO)4] insertion is probably an electrophilic C–Si cleavage reaction and that the process, using the term broadly, is concerted.

Reactions of strained organosilicon heterocycles with nonacarbonyldi-iron(0). Part 2. Preparation and reactions of silaferracyclopentanes

The formation of silaferracyclopentanes, by the reaction of silacyclobutanes with iron carbonyls, is described and their properties and reactions are discussed. The parent complex, 2,2,2,2-tetracarbonyl-1,1 -dimethyl-1 -sila-2- ferracyclopentane, has been prepared by the reaction of Me2[graphic omitted]CH2 with [Fe(CO)9](the preferred route) or, under u.v. irradiation, with [Fe(CO)5] or [Fe3(CO)12]; it has also been synthesised from Na2[Fe(CO)4] and SiMe2(CH2CH2CH2Cl)Cl. Analogues having aryl, alkoxy-, or chloro-substituents at silicon are described, together with derivatives of 1,1,3,3-tetramethyl-1,3-disilacyclobutane and two silabenzocyclobutenes. Infrared, 1H and 13C n.m.r., and mass spectroscopic data are discussed. Chemical properties of the silaferracyclopentanes are contrasted with those of the parent silacyclobutanes. The complex [graphic omitted]SiMe2)(CO)4] shows some activity as a hydrosilylation catalyst.