Andrew Hudson

Bulky alkyls, amides, and aryloxides of main Group 5 elements. Part 1. Persistent phosphinyl and arsinyl radicals ·MRR′ and their chloroprecursors MRR′Cl and related compounds

Interaction of LiR [R = CH(SiMe3)2 or N(SiMe3)2] and MCl3 in appropriate stoicheiometry affords the following new compounds: M[CH(SiMe3)2]Cl2 or M[CH(SiMe3)2]2Cl (M = P, As, or Sb), M[N(SiMe3)2]Cl2 or M[N-(SiMe3)2]2Cl (M = As or Sb), or Bi[N(SiMe3)2]3. Reaction of P(NPri2)Cl2 with Li[N(SiMe3)2]·OEt2, Li[N(CMe3)(SiMe3)], Li[CH(SiMe3)2], MgButBr, or NHPri2 yields the corresponding new compound P(NPri2)RCl, while Li[CH(SiMe3)2] with P(NMe2)Cl2 affords P[CH(SiMe3)2](NMe2)Cl. Reduction of the appropriate phosphorus(III) or arsenic(III) monochloride in toluene by photolysis with the olefin (Et[graphic omitted]Et gives the persistent (t½= 3 days to > 1 year in PhMe at 300 K) phosphorus(II) or arsenic(II) alkyl or amide: ·M[CH(SiMe3)2]2(M = P or As), ·M[N(SiMe3)2]2, ·P[CH(SiMe3)2](NR2)(R = Pri or SiMe3), ·P(NPri2)[N(SiMe3)2], ·P[N(CMe3)(SiMe3)]2, or ·P(NPri2)[N(CMe3)(SiMe3)]. Electron spin resonance parameters are discussed.

Synthesis and electron spin resonance study of stable dialkyls and diamides of phosphorus and arsenic, R12M· and (R22N)2M·

Photolysis of toluene solutions of dialkyl-phosphorus or -arsenic chlorides [(Me3Si)2CH]2MCl (M = P or As) or bisamido-phosphorus or -arsenic chlorides [(Me3Si)2N]2MCl (M = P or As) in the presence of an electron-rich olefin leads to solutions containing persistent (t½ > 1 month at 20 °C) two-co-ordinate phosphorus or arsenic-centred radicals [(Me3Si)2CH]2M· or [(Me3Si)2N]2M·(M = P or As) characterised by their e.s.r. spectra.

Tris[bis(trimethylsilyl)methyl]tin(III), R3Sn·: an unusually stable stannyl radical, from photolysis of R2Sn

Photolysis of R2Sn [R =(Me3Si)2CH] with visible light in benzene at ambient temperature yields the stable radical R3Sn·, which has an e.s.r. solution spectrum showing coupling with the methine protons and 119Sn and 117Sn nuclei.

Photolytic homolysis of metal–metal bonds of some binuclear transition-metal carbonyls: an electron spin resonance investigation using spin trapping

Irradiation, using a 250-W high-pressure mercury lamp, of a solution of [Mn2(CO)10] and an excess of nitrosodurene (RNO) in CH2Cl2 at ⩽–30 °C in the cavity of an e.s.r. spectrometer produces an 18-line signal attributed to [Mn(CO)5{Ṅ(O)R}]. Similarly, aminyl oxides derived from spin. trapping of [Mn(CO)4L][L = P(OPh)3, PPh3, PMePh2, PMe2Ph, PBun3, or P(C6H11)3], [Re(CO)5], [Co(CO)3{P(OEt)3}], [Mo(η-C5H5)(CO)2L][L = CO or PPh3], or [Fe(η-C5H5)(CO)2] have been characterised by their e.s.r. solution spectra at ca. –30 °C, g= 2.005–2.01. The nitrogen hypetfine coupling [a(14N)] is in the range 1.45–1.75 mT, while a(55Mn)= 0.82–0.89, a(185,187Re)= 4.09, a(59Co)= 1.39, a(95,97Mo)= 0.40–0.50, and a(31P)= 0.92–1.67 mT for the manganese complexes and 0.45 mT for [Co(CO)3{Ṅ(O)R}{P(OEt)3}]. For photolysis of [Mn(CO)10]: (i) formation of aminyl oxide requires light in the 300–400 nm region; (ii) using PhMe as solvent, or with CH2Cl2 but RNO as a minor component, a 31-line spectrum assigned to [{R(O)N}(OC)4MnMn(CO)5]+· is obtained. A mechanism is proposed whereby initial formation of [Mn(CO)5] is followed by competitive processes leading either to [Mn(CO)5{Ṅ(O)R}] or [Mn(CO)5]– and [Mn2(CO)10]+·. which finally may disproportionate to MnII–Mn–I or react with RNO to yield the binuclear metal aminyl oxide.

Generation and e.s.r. spectra of some new phosphorus-centred radicals Ṗ2Ar2X, Ṗ(Ar)X, Ṗ(OAr)2, ṖAr2(:O), ṖAr[N(SiMe3)2](:NSiMe3), and [P2Ar2]˙– derived from the bulky group C6H2But3-2,4,6(= Ar)

The photochemical reaction of X2 and the diphosphene trans-ArPPar (Ar = C6H2But3), (1) leads successively to Ṗ2Ar2X, (2), Ṗ(Ar)X, (3), and upon cooling [(Ar)X]2[for X = OBut, ΔHdiss= 107 ± 7kJ mol–1] for X = OBut or SPrn, whereas for X = SBut only (3) was detected; the radicals Ṗ(Ar)X, Ṗ(Oar)2, and Ṗ2(:O) were formed by reduction of the appropriate diamagnetic PIII or PV chloride, while [P2Ar2]˙– was obtained from (1) and Na[C10H8].

Homolysis of metal–carbon and metal–metal bonds: spin-trapping of the resulting carbon- and metal-centred radicals

Homolysis of the C–Mn bond of [RMn(CO)5] or [RCOMn(CO)5] under u.v. irradiation has been studied using nitrosodurene as a spin-trap for both the radicals formed; irradiation of various metal–metal bonded compounds (LM–ML, M = Mn, Re, Fe, Mo, or Co) gives rise to metal-centred radicals which can similarly be trapped.

Electron spin resonance of t-alkyl-, silyl-, and germyl-aminyl radicals and some observations on the amides MBr{N(SiMe3)2}3(M = Ge, Sn, or Pb)

The e.s.r. spectra of the π-radicals :NRR′(R = R′= GeMe3, SiEt3, or CMe3; or R = CMe3 and R′= SiMe3; or NR2= 2,2,6,6-tetramethylpiperidyl), obtained by photolysis of M(NRR′)2(M = Ge or Sn), are reported; the tetravalent title compounds, prepared by oxidative addition of BrN(SiMe3)2 to M′{N(SiMe3)2}2(M′= Ge, Sn, or Pb), are not sources of aminyls, but reduction of GeBr{N(SiMe3)2}3 provides a convenient route to Ge{N(SiMe3)2}3.

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)].

Subvalent Group 4B metal alkyls and amides. Part 4. An electron spin resonance study of some long-lived photochemically synthesised trisubstituted silyl, germyl, and stannyl radicals

A number of solution-stable species of general formula MR3˙[R = CH(SiMe3)2: M = Si. Ge. or Sn], M(NR′2)3˙ and M (NR′R″)3˙(R′= SiMe3, R″= CMe3, M = Ge or Sn) have been prepared and characterised by e.s.r. spectroscopy. Most of the radicals have been generated by photolysis of the bivalent Group 4 species MR, M(NR′2)2 or M(NR′R″)2 when available; others have been obtained by alternative photochemical experiments. The e.s.r. parameters indicate that the radicals have non-planar structures similar to those of analogous transient species such as MMe3˙. The mechanism of formation of the radicals is discussed : their unusual stability (e.g. SnR3˙ has a halflife of ca. 1 year at 20 °C) is attributed mainly to steric hindrance to dimerisation.

Photolytic homolysis of the metal–carbon (sp3 or sp2) bond of alkyl or acyl transition-metal complexes: an electron spin resonance study using spin trapping; and a note on aminyl oxides [MLn{N(Ȯ)R}][MLn= Ru(CO)4(SiMe3), Os(CO)4(SiMe3), or Fe(η-C3H5)(CO)3; R = aryl]

Irradiation of the following metal alkyls has been carried out in CH2Cl2(or PhMe) in the presence of nitrosodurene, RNO (R = C6HMe4-2,3,5,6), in the cavity of an e.s.r. spectrometer: [Mn(CO)5R′](R′= CH2Ph or CH2SiMe3), [Fe(η-C5H5)(CO)2R′], [Mo(η-C5H5)(CO)3R′](R′= Me, Et, or CH2Ph), cis-[PtR′2(PMe2Ph)2](R′= CH2SiMe3 or CH2CMe3), [AuR′(PPh3)](R′= Me or CH2SiMe3), and [CoR′L(oep)](H2oep = 2,3,7,8,12,13,17,18-octaethylporphyrin and R′= Me, L = NC5H5; or R′= Et, L = OH2). Similar experiments have been performed on (i) the acylmetal complexes [Mn(Co)5{C(O)R″}](R″= CH2Cl, Me, Et, CH2Ph, or CHPh2) or [Fe(η-C5H5)(CO)2{C(O)R″}](R″= Me or CH2Ph), and (ii) the metal–metal bonded [M2(CO)8(SiMe3)2](M = Ru or Os). Finally, the dark reaction between the stable iron(I) complex [Fe(η-C3H5)(CO)3] and RNO in CH2Cl2 has been investigated. As a consequence, from the alkyls, metallo-aminyl oxides [MLn{N(Ȯ)R}] were observed, except for MLn= a platinum(I), gold(0), or cobalt(II) moiety, but the alkylaminyl oxides RN(Ȯ)R′ were found in every case [although with the molybdenum(II) alkyls as substrates these were not detected at –30 °C but only at 20 °C]; two of these (R′= CH2SiMe3 or CH2CMe3) are new and show remarkably different β-proton hyperfine couplings, attributed in part to a conformational difference allowing for close Si ⋯ O proximity for R′= CH2SiMe3, and also to the greater steric requirements of the neopentyl group. From the acyls, the corresponding metallo-aminyl oxide was invariably detected, but never the spin-trapped acyl radical RN(Ȯ)COR″; however, the corresponding spin-trapped alkyl radical RN(Ȯ)R″ was observed but only for the case of R″= CH2Ph or CHPh2. The remaining experiments led to the e.s.r. characterisation of [MLn{N(Ȯ)R}], MLn= Ru(CO)4(SiMe3), Os(CO)4(SiMe3), or Fe(η-C3H5)(CO)3.