Marek Pakulski

Synthesis of a phospha-arsene and a phosphastibene; the first compounds with phosphorus–arsenic and phosphorus–antimony double bonds

The reaction of (Me3Si)2CHMCl2(M = As or Sb) with (2,4,6-But3C6H2)PH2 in the presence of 1,5-diazabicyclo[5.4.0]undec-5-ene affords the double-bonded compounds, (2,4,6-But3C6H2)PMCH(SiMe3)2(M = As or Sb)

Sulfur cleavage of a phosphorus-phosphorus double bond

Abstract Cleavage of the phosphorus-phosphorus double bond takes place when the diphosphene, (2,4,6-( t -Bu)3C6H2P)2, is treated with excess sulfur in the presence of DBU (1,5-diazabicyclo[5.4.0]undec-5-ene).

Notes. Oxidation and reduction of phosphorus–phosphorus and arsenic–arsenic double bonds. An electrochemical study of two diphosphenes and a diarsene

The diphosphenes [(Me3Si)3C]2P2(1) and (2,4,6-But3C6H2)2P2(2) and the diarsene [(Me3Si)3C]2As2(3) undergo electrochemical reduction in tetrahydrofuran (thf) solution to the corresponding anion radicals [{(Me3Si)2C}2P2]˙–(4), [(2,4,6-But3C6H2)2P2]˙–(5), and [{(Me3Si)3C}2As2]˙–(6), respectively. Anion radicals (4) and (5) were sufficiently stable to permit the acquisition of e.s.r. data. The products of oxidation of (1), (2), and (3) were much more difficult to characterise. The oxidation of (1) in CH2Cl2, is irreversible at 25 °C; however, at –75 °C a one-electron oxidation occurs to the unstable cation radical [{(Me3Si)3C}2P2]˙+. The oxidation of both (2) and (3) is irreversible even at –75 °C.

Arbuzov reaction of alkyl and silyl phosphites with halogens involving four- and five-co-ordinate intermediates

Low temperature 31P n.m.r. spectroscopy and chemical data have been applied to elucidate the mechanism of the Arbuzov-type reaction between phosphites and halogens. Simple and substituted trialkyl, alkyl 1,2-phenylene, and trisilyl phosphites have been allowed to react with chlorine, bromine, and iodine. In some cases intermediate halogenophosphonium salts (2) and in others halogenophosphoranes (3) are observed which then decompose into the corresponding pure highly reactive phosphorohalidates (4). It was possible to prepare stable phosphonium salts from halogenophosphonium salts (2) and halogenophosphoranes (3).

Synthesis and reactivity of mononuclear molybdenum phosphido complexes, [Mo(CO)2{P(Cl)R}(η-C5H5)][R = CH(SiMe3)2 or NCMe2CH2CH2CH2CMe2]. X-Ray crystal structures of [Mo(CO)2{P(X)(NCMe2CH2CH2CH2CMe2)}(η-C5H5)](X = Cl or NMe2) and [Mo2(CO)4{µ-P2[CH(SiMe3)2]2}(η-C5H5)2]

Reaction of K[Mo(CO)3(η-C5H5)] with PCl2R affords the mono-chlorophosphido species, [Mo(CO)2{P(Cl)R}(η-C5H5)][R = 2,2,6,6-tetramethyl-1-piperidyl (tmp), (1), or CH(SiMe3)2, (3)]. Both (1) and (3) contain a three-electron donor phosphido ligand featuring Mo–P multiple bonding and a trigonal-planar configuration at phosphorus. Compound (1) has been characterised by X-ray diffraction. The reaction of (1) with Li[NMe2] affords [Mo(CO)2{P(NMe2)(tmp)}(η-C5H5)](7), which has also been characterised by X-ray crystallography. The synthesis of (7) demonstrates the reactivity of the P–Cl functionality but (7) may also be prepared by direct reaction between K[Mo(CO)3(η-C5H5)] and PCl(NMe2)(tmp). Reduction of (3) with sodium dihydronaphthylide leads to a coupling reaction via P–P bond formation resulting in the cis-diphosphene complex [Mo2(CO)4{µ-P2[CH(SiMe3)2]2}(η-C5H5)2](8), which was characterised by X-ray diffraction. Spectroscopic evidence is also presented for a dimolybdenum diphosphinidene complex, isomeric with (8).

A novel diphosphorus-molybdenum ring system

Abstract The reaction of ArPCl2 (Ar = 2,4,6-t-Bu3C6H2) with K[Mo(CO)3(η-C5H5)] affords Ar(H)PP(Cl)Ar (1), ArP[Mo(CO)2(η-C5H5)]2 (2), ArPPAr, ArPH2 and Ar(H)PP(H)Ar. By means of X-ray crystallography, it was established that the Mo2P ring of 2 involves a planar phosphorus geometry, a slight degree of MoP multiple bonding, and a MoMo single bond. Thermolysis of the original reaction mixture produced the P2Mo ring compound ArPP(H)(Ar)[μ2-Mo(CO)2(η-C5H5)] (3). The structure of 3 was determined by X-ray diffraction.

The question of ‘open’ or ‘closed’ bimetallic phosphinidene (and heavier congeneric) complexes

The reaction of ArPCl2(Ar = 2,4,6-But3C6H2) with Na[Co2(µ2-CO)2(η-C5H5)2] affords the ‘open’ phosphinidene complex, Co2(µ2-PAr)(η-C5H5)2(CO)2, the structure of which has been determined by X-ray crystallography.

Novel insertion of the dioxophosphorane moiety (‘metaphosphonate’) into an aliphatic C–H bond via flash vacuum pyrolysis of a cyclic phosphonite and by oxidation of a diphosphene

Flash vacuum pyrolysis of 2-(2,4,6-tri-t-butylpheny)-1,3,2-dioxaphospholane (1) gave 5,7-di-t-butyl-3,3-dimethyl-2,3-dihydro-1-hydroxy-1λ5-benzophosphol-1-one (4), 100% also produced by photo-oxidation of bis (2,4,6-tri-t-butylphenyl)diphosphene (3)via insertion of the dioxophosphorane (–PO2) moiety into a neighbouring C–H bond.

A new approach to the formation of phosphorus–phosphorus double bonds

The reaction of (Me3Si)2CHPCl2 or (Me3Si)3CPCl2 with (2,4,6-But3C6H2)PH2 in the presence of DBU (1,5-diazabicyclo[5.4.0]undec-5-ene) affords the unsymmetrical diphosphene, (Me3Si)2CHPP(2,4,6-But3C6H2).

Determination of the gas-phase molecular structure of tris(trimethylsilyl)(trichlorosilyl) methane by electron diffraction

Abstract The molecular structure of tris(trimethylsilyl)(trichlorosilyl)methane in the gas phase has been determined by electron diffraction. The mean inner SiC distance ( r a ) is 190.9 (8) pm, with the difference between Me 3 SiC and Cl 3 SiC distances fixed at 2.3 pm. The outer SiCH 3 bonds are 187.8 (6) pm long, and r (SiCl) is 203.3 (6) pm. The SiCSi angles are close to tetrahedral, being 108.1 (6) ° between the Me 3 Si groups and 110.9(6)° between Me 3 Si and Cl 3 Si groups. Effects of steric crowding are seen mainly in the angles at the silicon atoms, with C(Me)SiC(Me) 107.0 (11)° and ClSiC 114.6 (11)°. All the SiX 3 groups are twisted by about 23° from the fully eclipsed configuration, in which the central C(SiX 3 ) 4 skeleton approximates to T d symmetry, reducing this to approximate T symmetry. This twisting minimises long-range interactions between the silyl groups.