Complexes of P-stabilised carbanions with s- and p-elements

From Stable PH-Ylides to α-Carbanionic Phosphines as Ligands for Zwitterionic Catalysts

Although ylides are commonly used reagents in organic synthesis, the parent methylphosphine MePH2 only exists in its phosphine form in the condensed phase. Its ylide tautomer H3 P+ -CH2 - is considerably higher in energy. Here, we report on the formation of bis(sulfonyl)methyl-substituted phosphines of the type (RO2 S)2 C(H)-PR2, which form stable PH ylides under ambient conditions, amongst the first examples of an acyclic phosphine which only exists in its PH ylide form. Depending on the exact substitution pattern the phosphines form an equilibrium between the PH ylide and the phosphine form or exist as one of both extremes. These phosphines were found to be ideal starting systems for the facile formation of α-carbanionic phosphines. The carbanion-functionalization leads to a switch from electron-poor to highly electron-rich phosphines with strong donor abilities and high basicities. Thus, the phosphines readily react with different electrophiles exclusively at the phosphorus atom and not at the carbanionic center. Furthermore, the anionic nature of the phosphines allows the formation of zwitterionic complexes as demonstrated by the isolation of a gold(I) complex with a cationic metal center. The cationic gold center allows for catalytic activity in the hydroamination of alkyne without requiring a further activation step.

Molecular 1,1'-bifunctional mixed-valence P-P compounds, enabled through metal complexation

Mixed-valence compounds feature the same atoms but in different formal oxidation states. This research field is largely dominated by metal-based solid-state chemistry and has been intensively studied in recent years. By contrast, the situation is different for molecular main group element compounds and to establish 1,1'-bifunctional groups remained a particular challenge. Here a detailed study on 1,1'-bifunctional mixed-valence main group compounds possessing a P-P bond is presented, and the fundamental role of the metal complex fragments is discussed. Based on the generation of a transient phosphanylidene-phosphinidenoid complex a dinuclear diphosphene complex was obtained possessing an unprecedented ambident reactivity, i.e., 1,2-addition or 1,1-addition products were obtained depending on the nature of the reagent. The 1,1-addition products represent stable hitherto unknown 1,1'-bifunctional phosphanylidene-phosphorane complexes which have been confirmed by X-ray diffraction studies. Detailed state-of-the-art DFT calculations provide insight into bonding and reaction pathways.

The importance of the Lewis base in lithium mediated metallation and bond cleavage reaction of allyl amines and allyl phosphines

Reactions of analogous N-allyl and P-allyl moietys with nBuLi and different Lewis donors was investigated resulting in contrasting reactivity. The N-allyl moieties favor deprotonation products while the P-allyl system result in competing P-allyl bond cleavage.

Direct synthesis of doubly deprotonated, dearomatised lutidine PNP Cr and Zr pincer complexes based on isolated K and Li ligand transfer reagents

Double deprotonation of a hybrid bis(phosphino)picoline ligand yields lithium or potassium pincer salts with dearomatised lutidine backbones that afford unusual chromium and zirconium complexes by transmetallation.

Instability of metal 1,3-benzodi(thiophosphinoyl)methandiide complexes: formation of hafnium, tin and zirconium complexes of 1,3-benzodi(thiophosphinoyl)thioketone dianionic ligand [1,3-C6H4(PhPS)2CS]2−

The reaction illustrates that the metal centre and ligand substituents are crucial for the stabilization of a C_methandiideHf bond.

Syntheses, structures and flexible coordination of sterically demanding di- and “tri”-lithiated methandiides

Sequential lithiation of a sterically demanding bis(iminophosphoranyl)methane afforded di- and trianionic methandiide lithium complexes and their structures and coordination behaviour have been studied with solid state and solution methods.

Formation of a Ph2PCH(BH3)P(BH3)Ph2 ligand via formal 1,2-borane migration

The transfer of the anionic Ph(2)P(BH(3))-CH-P(BH(3))Ph(2) ligand from potassium to barium results in the subsequent formation of a tetranuclear barium cluster which contains the hitherto unknown isomeric form Ph(2)P-CH(BH(3))-P(BH(3))Ph(2) of the ligand.

P[N(i-Bu)CH(2)CH(2)](3)N: nonionic Lewis base for promoting the room-temperature synthesis of α,β-unsaturated esters, fluorides, ketones, and nitriles using Wadsworth-Emmons phosphonates

The bicyclic triaminophosphine P(RNCH(2)CH(2))(3)N (R = i-Bu, 1c) serves as an effective promoter for the room-temperature stereoselective synthesis of α,β-unsaturated esters, fluorides, and nitriles from a wide array of aromatic, aliphatic, heterocyclic, and cyclic aldehydes and ketones, using a range of Wadsworth-Emmons (WE) phosphonates. Among the analogues of 1c [R = Me (1a), i-Pr (1b), Bn (1d)], 1a and 1b performed well, although longer reaction times were involved, and 1d led to poorer yields than 1c. Functionalities such as cyano, chloro, bromo, methoxy, amino, ester, and nitro were well tolerated. We were able to isolate and characterize (by X-ray means; see above) the reactive WE intermediate species formed from 2b and 1c.

Mixed donor-functionalised phosphinomethanide complexes of the alkali metals; synthesis, structures, and solution dynamics

The mixed donor tertiary phosphine {(Me(3)Si)(2)CH}P(C(6)H(4)-2-CH(2)NMe(2))(C(6)H(4)-2-CH(2)OMe) (11) is accessible via the stepwise addition of [Li(C(6)H(4)-2-CH(2)NMe(2))] followed by [Li(C(6)H(4)-2-CH(2)OMe)] to the dichlorophosphine {(Me(3)Si)(2)CH}PCl(2). Phosphine 11 is readily deprotonated by Bu(n)Li to give the lithium phosphinomethanide [[{(Me(3)Si)(2)C}P(C(6)H(4)-2-CH(2)NMe(2))(C(6)H(4)-2-CH(2)OMe)]Li] (15), which undergoes metathesis reactions with the alkoxides MOBu(t) [M = Na, K] to give the heavier alkali metal phosphinomethanides [[{(Me(3)Si)(2)C}P(C(6)H(4)-2-CH(2)NMe(2))(C(6)H(4)-2-CH(2)OMe)]M(L)(n)](x) in good yield [M = Na (12), (L)(n) = Et(2)O, x = 1; M = K (13), n = 0, x = 2]. Compounds 12 and 13 adopt monomeric and dimeric structures, respectively, in the solid state. Variable-temperature NMR studies indicate that compounds 12 and 13 are highly fluxional in solution; this fluxionality arises from a dynamic equilibrium between two conformers, which differ in the orientation of the aromatic rings of the ligand. The nature of these conformers and their relative energies have been probed by DFT calculations, which show the two principal conformers to differ in energy by just 1.6 kcal mol(-1). Calculation of the (1)H NMR shielding tensors using the GIAO method reveals that the low field chemical shifts of one benzylic and one aromatic proton in the ground state conformer are due to their close proximity to the carbanion centre.

{μ-[2-(Dimethyl-amino)phen-yl](2-fluoro-phen-yl)methano-lato}penta-methyl-dialuminum(III)

Each of the Al atoms in the title compound, [Al₂(CH₃)₅(C₁₅H₁₅FNO)], is four-coordinated in a distorted tetra­hedral geometry. The dimethyl­aluminium centre is bound by the N and the O atoms of the (2-dimethyl­amino­phen­yl)(2-fluoro­phen­yl)methano­late ligand. The second Al atom is bound by the methano­late O atom and by three methyl C atoms. The crystal studied was a racemic twin with a 0.4 (2):0.6 (2) domain ratio.

Effect of peripheral donor substituents on the binding modes of phosphinomethanide ligands. Synthesis and crystal structures of alkali metal derivatives of an O-functionalised phosphinomethanide ligand

The O-functionalised tertiary phosphine {(Me3Si)2CH}P(C6H4-2-CH2OMe)2 (9) is accessible via the reaction of {(Me3Si)2CH}PCl2 with two equivalents of in situ generated 2-LiC6H4CH2OMe. Phosphine 9 is readily deprotonated by Bu(n)Li to give the lithium phosphinomethanide [[{(Me3Si)2C}P(C6H4-2-CH2OMe)2]Li] (13), which undergoes metathesis reactions with the alkoxides MOR [M = Na, K, R = Bu(t); M = Rb, R = 2-ethylhexyl] to give the heavier alkali metal phosphinomethanides [[{(Me3Si)2C}P(C6H4-2-CH2OMe)2]M]n in good yields [M = Na (14), n= 2; M = K (15), Rb (16), n=[infinity]]. Compounds 9, [{(Me3Si)2CH}P(C6H4-2-CH2OMe)2LiBr]2 (10), and 14-16 have been studied by X-ray crystallography; in the solid state 14 adopts a dimeric structure, whereas 15 and 16 crystallise as one-dimensional polymers.

New bidentate cationic and zwitterionic relatives of Crabtree's hydrogenation catalyst

Inspired by the monodentate P,N ligation strategy featured in Crabtree's catalyst [(COD)Ir(PCy3)(Py)]+PF6-([1]+PF6-), a new class of bidentate cationic ([2]+X-) and zwitterionic (3) Ir complexes have been developed, which are capable of mediating the hydrogenation of alkenes under mild conditions and in a wider range of solvents than is possible for [1]+PF6-.