Electrochemical approaches to generation of phosphinidene complexes of tungsten pentacarbonyl

An alternative approach to synthesis of electrophilic terminal phosphinidene complexes of tungsten pentacarbonyl with various substituents at the phosphorus atom has been developed. The approach is based on the reaction of the electrochemically generated tungsten pentacarbonyl ion with trivalent phosphorus acyl chlorides. Electrochemical reduction of ethyldichlorophosphines in the presence of α-diimines is a one-step process that forms 1,3,2-diazaphospholenes containing an exocyclic P-C bond.     

Isolation of a 16π-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C4P2 Ring

Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADC^Ph)P]₂ ( 5-Ph ) (ADC^Ph=PhC{(NDipp)C}₂; Dipp=2,6-iPr₂C₆H₃) derived from an anionic dicarbene (ADC^Ph) as a red crystalline solid. Compound 5-Ph containing a 16π-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADC^Ph)PCl₂]₂ ( 4-Ph ) with Mg (or KC₈) in a quantitative yield. Experimental and computational results imply that the central 8π-electrons C₄P₂ ring of 5-Ph , which is fused between two 6π-electrons C₃N₂ aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5-Ph has two electron-lone-pairs, one in a p-type orbital is in conjugation with the C=C bonds of the C₄P₂ ring, while the second resides in a σ-symmetric orbital. This can be shown with the gold complex [(ADC^Ph)P(AuCl)₂]₂ ( 6-Ph ) obtained by reacting 5-Ph with (Me₂S)AuCl. A mixture of 5-Ph and 4-Ph undergoes comproportionation in the presence of MgCl₂ to form the intermediate oxidation state compound [(ADC^Ar)P]₂(MgCl₄) ( 7-Ph ), which is an aromatic species.     

Silanylidene and Germanylidene Anions: Valence‐Isoelectronic Species to the Well‐Studied Phosphinidene

The reduction of TipMCl₃ (Tip=2,4,6‐triisopropylphenyl) (M=Si, Ge) with KC₈ in the presence of cyclic alkyl(amino) carbene (cAAC) afforded the acyclic silanylidene and germanylidene anions in the form of potassium salt [K(cAAC)MTip]₂ (M=Si ( 1 ); Ge ( 2 )). The silanylidene and germanylidene anions are valence‐isoelectronic to the well‐studied phosphinidene and are a new class of acyclic anions of Group 14. Compounds 1 and 2 were isolated and well characterized by NMR and single‐crystal X‐ray structure analysis. Furthermore, the structure and bonding of compounds 1 and 2 was investigated by computational methods.     

Direct Conversion from Terminal Borylene into Terminal Phosphinidene

The first terminal manganese phosphinidene complex was quantitatively synthesized from a terminal alkylborylene complex. Its structure and bonding, as well as the reaction mechanism, were investigated through a combination of experimental and computational studies.     

Bidentate phosphorus baskets by intramolecular phosphinidene addition

Intramolecular phosphinidene addition to the C==C bond of Mo-complexed, seven-membered phosphorus heterocycles affords three novel [(diphos)Mo(CO)(4)] complexes (18-20). The three bidentate phosphorus baskets differ in the composition of the seven-membered ring: one of the phosphorus atoms is flanked by CH(2), NCH(3), or O. The unsaturated tetrahydrophosphepine precursors are synthesized by either ring-closing metathesis (C and N derivatives) or by a cyclization sequence (O derivative). The crystal structures of the nitrogen- (19) and oxygen-containing (20) baskets have relatively small P-Mo-P angles of 76.240(13) degrees and 77.626(12) degrees , respectively, and complex 20 has slightly shortened Mo--P bond lengths.     

‘Phospha-variations’ on the themes of Staudinger and Wittig: phosphorus analogs of Wittig reagents

The Wittig and Aza-Wittig reactions have undergone tremendous development over the past 50 years in light of their potential in organic synthesis to construct carbon–carbon and carbon–nitrogen double bonds. In contrast, the development of the analogous phospha-Wittig reaction has only seen progress over the last 12 years. A phospha-Wittig process is one that uses phosphaylides to convert carbonyl compounds to new materials possessing phosphorus–carbon double bonds (phosphaalkenes). The phospha-Wittig reaction has evolved from initial work involving metal-assisted phospha-Wittig reactions to phospha-Wittig reactions, of terminal phosphinidene complexes to, more recently, free phosphanylidene-σ⁴-phosphoranes as phospha-Wittig reagents. The major developments in the phospha-Wittig reaction are highlighted and divided into these three methodologies. The complementary nature and the differences between the three approaches is also discussed. Finally, wherein applicable, comparisons between the Wittig reaction and the phospha-Wittig reaction are presented.     

Synthesis and Coordination Ability of a Donor-Stabilised Bis-Phosphinidene

Chelating phosphines have long been a mainstay as efficient directing ligands in transition-metal catalysis. Low-valent derivatives, namely chelating phosphinidenes, are to date unknown, and could lead to chelating complexes containing more than one metal centre due to the intrisic capacity of phosphinidenes to bind two metal fragments at one P-centre. Here we describe the synthesis of the first such chelating bis-phosphinidene ligand, XantP₂ ( 2 ), generated by the reduction of a diphosphino xanthene derivative, Xant(PH₂)₂ ( 1 ) with ^iPrNHC (^iPrNHC=[:C{N(iPr)C(H)}₂]). Initial studies have shown that this novel chelating ligand can act as a bidentate ligand towards element dihalides (i.e. FeCl₂, ZnI₂, GeCl₂, SnBr₂), forming cationic complexes with the tetryl elements. In contrast, XantP₂ demonstrates an ability to bind multiple metal centres in the reaction with CuCl, leading to a cationic Cu₃P₃ ring complex, with Cu centres bridged by phosphinidene arms. Density Functional Theory calculations show that 2 indeed holds 4 lone pairs of electrons, shedding further light on the coordination capacity for this novel ligand class through observation of directionality and hybridisation of these electron pairs.