Formation and properties of phosphaquinomethane tungsten(0) complexes - isolation and conversion of primary radical coupling products.

A rational approach to phosphaquinomethane metal(0) complexes, based on dearomatization of the phenylene unit in [W(CO)](R)P(Cl)-CH-CPh, is described, including theoretical studies on mechanisms and structures. Furthermore, the first phosphaquinone tungsten complex with reversible redox properties is reported thus illustrating the beneficial stabilization of ligation.

N-Heterocyclic Carbene-Stabilized Germanium and Tin Analogues of Heavier Nitriles: Synthesis, Reactivity, and Catalytic Application.

The synthesis of stable heavier analogues of nitriles as monomeric tetrylene-phosphinidenes TerEP(IDipp) (E = Ge, Sn; Ter = 2,6-MesCH, IDipp = C([N-(2,6-PrCH)CH]) was achieved by taking advantage of NHC (N-heterocyclic carbene, here IDipp) coordination to the low-valent phosphorus center. Multiple bonding character of the E-P bonds was examined experimentally and computationally. Both germanium and tin compounds undergo [2+2] cycloaddition with diphenylketene, whereas reaction of the tin derivative with (pentafluorophenyl)borane provided unique "push-pull" phosphastannene (Ter)(Ar)Sn = P(IDipp) (Ar = CF[B(F)(CF)]).

The Quest for Stable Silaaldehydes: Synthesis and Reactivity of a Masked Silacarbonyl.

The first donor-acceptor complex of a silaaldehyde, with the general formula (NHC)(Ar)Si(H)OGaCl (NHC=N-heterocyclic carbene), was synthesized using the reaction of silyliumylidene-NHC complex [(NHC) (Ar)Si]Cl with water in the presence of GaCl . Conversion of this complex to the corresponding silacarboxylate dimer [(NHC)(Ar)SiO GaCl ] , free silaacetal ArSi(H)(OR) , silaacyl chloride (NHC)(Ar)Si(Cl)OGaCl , and phosphasilene-NHC adduct (NHC)(Ar)Si(H)PTMS unveil its true potential as a synthon in silacarbonyl chemistry.

NHCs in Main Group Chemistry.

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds.

Advances in Phosphasilene Chemistry.

Heavier alkene analogues possess unique electronic properties and reactivity, encouraging multidisciplinary research groups to utilize them in the rational design of novel classes of compounds and materials. Phosphasilenes are heavier imine analogues, containing highly reactive Si=P double bonds. Recent achievements in this field are closely related to the progress in the chemistry of stable low-coordinate silicon compounds.

Strong Evidence of a Phosphanoxyl Complex: Formation, Bonding, and Reactivity of Ligated Phosphorus Analogues of Nitroxides.

Facile access to [W(CO) (Ph P-OTEMP)] is used to initiate a study on the generation, properties, and reactions of transient phosphanoxyl complexes [ML (R PO)], the first example of which could be trapped via heterocoupling with the trityl radical. It is also demonstrated that the phosphorus nitroxyl complex acts as radical initiator in the polymerization of styrene. The quest for P-O versus O-N bond homolysis, as well as the initial steps of the polymerization were studied by DFT methods.

Synthesis of a 1-Aryl-2,2-chlorosilyl(phospha)silene Coordinated by an N-Heterocyclic Carbene.

Phosphasilenes, P=Si doubly bonded compounds, have received considerable attention due to their unique physical and chemical properties. We report on the synthesis and structure of a chlorophosphasilene coordinated by an -heterocyclic carbene (NHC), which has the potential of functionalization at the Si-Cl moiety. Treatment of a silylphosphine, ArPH-SiCl₂R (Ar = bulky aryl group, R = Si(SiMe₃)₃) with two equivalents of Im-Me₄ (1,3,4,5-tetramethylimidazol-2-ylidene) afforded the corresponding NHC-coordinated phosphasilene, ArP=SiClR(Im-Me₄) as a stable compound.

Selective phosphanyl complex trapping using TEMPO. Synthesis and reactivity of P-functional P-nitroxyl phosphane complexes.

Open-shell phosphanyl complexes (OC)5W{(Me3Si)2HCP(X)} (X = F, H), obtained by one-electron oxidation of lithium phosphanido complexes, were trapped by TEMPO to yield novel thermally labile P-nitroxyl phosphane complexes. First experimental evidence for an open-shell P-F phosphanoxyl complex (OC)5W{(Me3Si)2HCP(O)F}, formed upon thermolysis of corresponding P-nitroxyl derivative, is reported; reaction pathways are also theoretically investigated.

Synthesis and reaction of the first 1,2-oxaphosphetane complexes.

While P(V) 1,2-oxaphosphetanes are well known from the Wittig reaction, their P(III) analogues are still unexplored. Herein, the synthesis and reactions of the first 1,2-oxaphosphetane complexes are presented, which were achieved by reaction of the phosphinidenoid complex [Li(12-crown-4)(solv)][(OC)5W{(Me3Si)2HCPCl}] with different epoxides. The title compounds appeared to be stable in toluene up to 100 °C, before unselective decomposition started.

A novel N,P,C cage complex formed by rearrangement of a tricyclic phosphirane complex: on the importance of non-covalent interactions.

The reaction of Li/Cl P-CPh3 phosphinidenoid tungsten(0) complex 2 with dimethylcyanamide afforded tricyclic phosphirane complex 4, an unprecedented rearrangement of which led to the novel N,P,C cage complex 6. On the basis of DFT calculations, formation and intramolecular [3+2] cycloaddition of the transient nitrilium phosphane ylide complex 3 to a phenyl ring of the triphenylmethyl substituent to give 4 is proposed. Furthermore, theoretical evidence for terminal N-amidinophosphinidene complex 7, formed by [2+1] cycloelimination from 4, is provided, and the role of the electronic structure and non-covalent interactions of intermediate 7 discussed.

Synthesis and reactions of the first room temperature stable Li/Cl phosphinidenoid complex.

P-Trityl substituted Li/Cl phosphinidenoid tungsten(0) complex (OC)5W{Ph3CP(Li/12-crown-4)Cl} (3) was prepared via chlorine/lithium exchange in complex (OC)5W{Ph3CPCl2} (2) using (t)BuLi in the presence of 12-crown-4 in tetrahydrofuran (THF) at low temperature; complex 3 possesses significantly increased thermal stability in contrast to previously reported analogue derivatives. Terminal phosphinidene-like reactivity of 3 was used in reactions with benzaldehyde and isopropyl alcohol as oxaphosphirane complex (OC)5W{Ph3CPC(Ph)O} (5) and phosphinite complex (OC)5W{Ph3CP(H)O(i)Pr} (6) were obtained selectively. Reaction of 3 with phosgene allowed to obtain the first kinetically stabilized chloroformylphosphane complex (OC)5W{Ph3CP(Cl)C(O)Cl} (4).

An unusal case of facile non-degenerate P-C bond making and breaking.

Oxidation of Li/X phosphinidenoid complex 2, obtained via selective deprotonation from the P-H precursor 1, with [Ph(3)C]BF(4) led to the formation of two P-F substituted diorganophosphane complexes 6,7; the latter tautomer 7 formed via H-shift from 6. In contrast, oxidation of 2 with [(p-Tol)(3)C]BF(4) led to three major and one minor intermediates at low temperature, which we tentatively assign to two pairs of P-C atropisomers 10 a,a' and 10 c,c' and which differ by the relative orientations of their CH(SiMe(3))(2) and W(CO)(5) groups. Conversion of all isomers led finally to complex 11 having a ligand with a long P-C bond to the central trityl* carbon atom, firmly established by single-crystal X-ray analysis.