No abstract

Reduction of [CpFe(μ-Br)] (1, Cp = C(CH-4-Et)) by potassium napthalenide, followed by the addition of white phosphorus, affords [K(18-c-6){CpFe(η-P)}] (2, 18-c-6 = [18]crown-6), which features a planar cyclo-P ligand. The related diiron complex [Na(THF)(CpFe)(μ,η-P)] (3) was obtained by reducing 1 with sodium amalgam in the presence of P. Protonation of 3 affords [Na(THF)][(CpFe)(μ,η-P)(H)] (4), while the reaction of 3 with trimethylchlorosilane gives the nortricyclane compound P(SiMe) as the main product.

Oxidative addition of the P‒P single bond of an ortho-carborane-derived 1,2-diphosphetane (1,2-C2(PMes)2B10H10) (Mes = 2,4,6-Me3C6H2) to cobalt(-I) and nickel(0) sources affords the first heteroleptic complexes of a carborane-bridged bis(phosphanido) ligand....

New iron complexes [Cp*FeL]− (1‐σ and 1‐π, Cp*=C5Me5) containing the chelating phosphinine ligand 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine (L) have been prepared, and found to undergo facile reaction with CO2 under ambient conditions. The outcome of this reaction depends on the coordination mode of the versatile ligand L. Interaction of CO2 with the isomer 1‐π, in which L binds to Fe through the phosphinine moiety in an η5 fashion, leads to the formation of 3‐π, in which CO2 has undergone electrophilic addition to the phosphinine group. In contrast, interaction with 1‐σ—in which L acts as a σ‐chelating [P,N] ligand—leads to product 3‐σ in which one C=O bond has been completely broken. Such CO2 cleavage reactions are extremely rare for late 3d metals, and this represents the first such example mediated by a single Fe centre.

Salt metathesis of 1‐methyl‐2,4,6‐triphenylphosphacyclohexadienyl lithium and chlorobis(pentafluorophenyl)borane affords a 1‐phospha‐7‐bora‐norbornadiene derivative 2 . The C≡N triple bonds of nitriles insert into the P−B bond of 2 with concomitant C−B bond cleavage, whereas the C≡C bonds of phenylacetylenes react with 2 to form λ 4 ‐phosphabarrelenes. Even though 2 must formally be regarded as a classical Lewis adduct, the C≡N and C≡C activation processes observed (and the mild conditions under which they occur) are reminiscent of the reactivity of frustrated Lewis pairs. Indeed, NMR and computational studies give insight into the mechanism of the reactions and reveal the labile nature of the phosphorus–boron bond in 2 , which is also suggested by detailed NMR spectroscopic studies on this compound. Nitrile insertion is thus preceded by ring opening of the bicycle of 2 through P−B bond splitting with a low energy barrier. By contrast, the reaction with alkynes involves formation of a reactive zwitterionic methylphosphininium borate intermediate, which readily undergoes alkyne 1,4‐addition.

The coordination chemistry of phosphinines (phosphabenzenes) has been intensively investigated over the last decades, but metal complexes of halophosphinines and related halide-substituted phosphacyclohexadienyls have remained scarce.

The neutral, homoleptic pyridylphosphininenickel(0) complex 6-Ph 2 -PC 5 H 2 ) 2 ] (1) has been obtained by reaction of the formal Ni(0) source [(IPr)Ni(H 2 CCHSiMe 3 ) 2 ] with 2 equiv of 2-(2′-pyridyl)-4,6-diphenylphosphinine (L). Compound 1 can be oxidized both electrochemically and through the use of ferrocenium salts, to afford the corresponding Ni(I) complexes [1]BF 4 , [1(THF)]PF 6 , and [1 2 ](BAr F 4 ) 2 . The structures of these salts reveal an interesting dependence on the nature of the anion. While [1]BF 4 and [1(THF)]PF 6 show trigonal-bipyramidal coordination of Ni in the solid state, [1 2 ](BAr F 4 ) 2 exists as a dinuclear Ni(I) complex and possesses a bridging phosphinine moiety in a rare μ 2 mode. Reactions of 1 with halobenzenes highlight the noninnocent behavior of the aromatic phosphinine ligand, leading to the formation of oxidized Ni complexes but not to classical oxidative addition products. The reaction of 1 with bromobenzene affords the λ 5 phosphinine 2 and the bipyramidal Ni(I) complex [1]Br, whereas a more unconventional oxidation product 3 is formed from the reaction of 1 and iodobenzene.

The ability of phosphacyclohexadienyl anions [Li(1-R-PC 5 Ph 3 H 2 )] [R = Me (1 a), nBu (1 b), tBu (1 c), Ph (1 d) and CH 2 SiMe 3 (1 e)] to initiate hydrofunctionalisation reactions was investigated and compared with simple, commercially available compounds, such as LiOtBu, KOtBu and nBuLi. All compounds are expedient catalysts for the hydroboration of a wide scope of substrates, ranging from aldehydes to imines and esters. In the hydroboration of carbon dioxide, however, only our system was observed to efficiently produce the desired methanol equivalents.