R. V. (Dick) Parish

Organosilicon chemistry. Part 26. Silyl derivatives of substitued cobalt carbonyls of the type [Co(SiR3)(CO)n L4–n]

The series of cobalt(I) silyl complexes [Co(SiR3)(CO)n L4–n](R = F, n= 1–3; R = Ph or OEt, n= 2 or 3; L = tertiary phosphine or arsine) has been prepared, and the reaction of [Co(SiR3)(CO)4] with PPh3 has been studied. For R = Ph, substitution of CO occurs rapidly to give the unstable cis-[Co(SiPh3)(CO)3(PPh3)], which isomerises slowly to the stable trans form. For R = Et, however, decomposition occurs to give Si2Et6 and [{Co(CO)3(PPh3)}2]. Three distinct geometric isomers of [Co(SiR3)(CO)2 L2] have been obtained by different preparative routes.

Organosilicon chemistry. Part 24. Homogeneous rhodium-catalysed hydrosilation of alkenes and alkynes: the role of oxygen or hydroperoxides

The hydrosilation of propene, hex-1-ene, and hex-1-yne, catalysed by [RhCl(PPh3)3] has been reinvestigated. When all reagents are carefully purified, the hydrosilation reaction is completely inhibited but can be initiated by the addition of oxygen or t-butyl hydroperoxide. The rate and extent of reaction in the latter case is unaffected by the presence of phenolic radical traps. For optimum reaction, stoicheiometric quantities of hydroperoxide are required. In the hex-1-yne system, variation of the PPh3: Rh ratio gives maximum activity at 1 : 1 and, with this stoicheiometry, the reaction rate is relatively insensitive to purification of the reagents. It is suggested that the role of oxygen or hydroperoxide is to remove triphenylphosphine from the system, by oxidation, generating a highly active catalyst with a low PPh3: Rh ratio. In the ‘clean’ conditions isomerisation of hex-1-ene proceeds rapidly, being catalysed by the silyl complex [RhH(Cl)(SiR3)(PPh3)2].

Organosilicon chemistry. Part 23. Some silylcobalt(III) complexes and the homogeneous catalysis of deuteriation, hydrosilylation, and O-silylation reactions

The complexes [CoH(X2)L3](X = H or N; L = PPh3) react with silanes, SiR3H, to give the new silylcobalt(III) complexes [CoH2(SiR3)L3][R3= F3, MeF2, or (OEt)3]. The characterization of these complexes and their reactions with N2, H2, HCl, CCl4, and CO are described. With CO the new cobalt(I) silyl [Co(SiF3)(CO)2L2] is formed. The stability of the silyls to loss of SiR3H decreases as the electronegativity of R decreases, which allows the less-stable complexes to participate in catalytic processes. The reaction of SiR3H with D2(R = F, OEt, Et, or Me), of SiH(OEt)3 or Me3Si[OSi(H)Me]nOSiMe3 with EtOH, and of SiH(OEt)3 with hex-1-ene are catalysed by [CoH(X2)L3] or by [CoH2{Si(OEt)3}L3]. The deuteriation reaction provide an easy routr to deuteriosilanes, SiR3D.

Reactions involving transition metals. Part IX. The structure and isomerism of some dihalogenohydridotris(ligand)rhodium(III) complexes

The isomers α- and β-[L3RhHX2](L = tertiary phosphine or arsine. X = Cl or Br) are shown to have the same structures as the corresponding iridium complexes, i.e. a mer-configuration for the neutral ligands and hydride trans to halogen (α-form) or to the neutral ligand (β-form). The isomerisation β→α is enhanced by heat and light, but is inhibited in the presence of the free neutral ligand. indicating a dissociative mechanism. The bulky ligands Phn(C6H11)3–nP (n= O–3) and Ph3As give products of variable stoicheiometry but only two neutral ligands appear to be co-ordinated to the metal.

Organosilicon chemistry. Part 25. Catalysis of the reaction between alcohols and silanes by hydrido-, dinitrogen-, and ethylene-iron complexes

The reaction between alcohols, ROH (R = Me, Et, Prn, or Bun), and SiH(OEt)3 or SiPh2H2 is strongly catalysed at room temperature by [FeH2(PMePh2)4] or by [FeH2(N2)(PEtPh2)3]. With SiH(OEt)3, reaction is complicated by alkoxy-exchange when R ≠ OEt. With both catalysts the reactions have induction periods but are thereafter first order in the concentration of each of the reactants and of the catalyst. Mechanisms are proposed based on the formation of iron–silyl complexes. The complex [Fe(C2H4)(dppe)2](dppe = Ph2PCH2CH2PPh2) also catalyses the reaction but is rapidly deactivated by conversion into [FeH2(dppe)2].

Reactions involving transition metals. Part XI. Reactions of nucleophiles with dieneplatinum complexes

The reactions of the complexes [Pt(diene)Cl2](diene = norbornadiene or dicyclopentadiene) with the nucleophiles OPri–, NH2Ph, SPh–, and SCN– have been investigated. The dicyclopentadiene complex undergoes attack at the diene in each case and the S-nucleophiles also give substitution at platinum. Onlythelatterreactionoccurswith the norbornadiene complexes and S-nucleophiles, but attack on the organic ligand is found with OPri– and NH2Ph, The reactions of these products with neutral uni- and bi-dentate ligands usually leads to bridge-splitting reactions, but in some cases the norbornenyl derivatives undergo rearrangement to nortricyclene systems. The reaction of the alkenyl complexes with a further nucleophile (OMe– or NHPh–) to give doubly σ-bonded alkyleneplatinum complexes is described.

Reactions involving transition metals. Part X. Reactions of the complexes α- and β-[L3RhHX2](L = tertiary phosphine or arsine, X = Cl or Br)

The reactions of the complexes α- and β[LnRhHX2](n= 2 or 3; L = tertiary phosphine or arsine; X = Cl or Br) with acidic, basic, oxidising, and reducing reagents have been investigated. The α-isomers are inert to acids (except nitric acid) but are rapidly dehydrohalogenated by bases. With weak bases, equilibria are established, the positions of which show that stability to dehydrohalogenation increases in the series L = Ph2RP < PhR2P < R3P, R = Et < Me (n= 3) and L = Ph3P < Ph3 As < Ph3Sb (n= 2). The β-isomers react similarly with bases and give trihalogeno-complexes with hydrogen halides. With sulphur dioxide both isomers are reduced and.form the SO2 complexes [L3RhXSO2]·HX (X = Cl or Br). Both isomers also react with nitric acid to give [L2 RhX2NO3].

Organosilicon chemistry. Part XII. Stability and catalytic activity of some chlorohydridobis(phosphine)(silyl)rhodium(III) complexes

New complexes of the type [L2RhH(SiR3)Cl] have been prepared [L = Ph2(tol)P, Ph2(cy)P, Ph(cy)2P, or Ph2PriP; R = OEt, Me, or Et; tol =p-tolyl; cy = cyclohexyl]. Evidence for similar complexes with L = Ph2EtP and Ph2MeP has been obtained by ligand-exchange studies. The stability to dissociation of complexes of this type increases in the orders SiMe3 < SiMe2Cl < SiMeCl2 < SiCl3, SiPh3 < SiEt3 < Si(OEt)3 < SiCl3, (cy)3P < Ph(cy)2P < Ph2(cy)P ≲ Ph2(tol)P ≈ Ph3P, Ph2MeP < Ph2EtP < Ph2PriP ≈ Ph3P, and Ph3As < Ph3P. The dependence of stability on the neutral ligand reflects a combination of steric and electronic effects. The rate of addition of triethylsilane to hex-1-ene, catalysed by the complexes [L3RhCl], increases in the order L =(cy)3P Ph2MeP < Ph(cy)2P ≈ Ph3P < Ph2(cy)P ≈ Ph2EtP.