Low-valent homobimetallic Rh complexes: influence of ligands on the structure and the intramolecular reactivity of Rh-H intermediates.

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. Their reaction with hydrogen rapidly forms Rh hydrides that undergo an intramolecular semihydrogenation of two C[triple bond, length as m-dash]C bonds of the trop ligand. This reaction is chemoselective and converts C[triple bond, length as m-dash]C bonds to a bridging carbene and an olefinic ligand in the first and the second semihydrogenation steps, respectively. Stabilization by a bridging diphosphine ligand allows characterization of a Rh hydride species by advanced NMR techniques and may provide insight into possible elementary steps of H2 activation by interfacial sites of heterogeneous Rh/C catalysts.

Phosphanyl Cyanophosphide Salts: Versatile PCN Building Blocks.

The facile preparation of alkali salts of phosphanyl cyanophosphides [NHP-PCN]- (NHP=N-heterocyclic phosphenium) is reported. Their formation is achieved by isoelectronic replacement of O for [N]- in the phosphaketenes NHP-PCO using alkaline hexamethyldisilazide M[N(SiMe3 )2 ] (M=Na, K) as reagent. The new anionic entities are versatile PCN building blocks which allow the formation of a diversity of new cyanophosphine derivates including the first example of a PCNB hetero-cumulene and a PCN-ligated transition metal complex.

Salen supported Al-O-C[triple bond, length as m-dash]P and Ga-P[double bond, length as m-dash]C[double bond, length as m-dash]O complexes.

The first OCP adducts of aluminium and gallium are reported. The complexes are supported by sterically encumbered salen ligands and reveal a selective binding to O and P, respectively. Their reactivity with diazaphosphenium Lewis acids and N-heterocyclic carbene Lewis bases is described, in addition to cycloaddition reactions with s-tetrazines.

Transient Dipnictyl Analogues of Acrylamides, R-E=E'-CONR2 , and a Related Diphosphadigalletane from Na[OCP] and (R2 N)2 ECl (E, E'=P, As, Ga).

The reaction of Na[OCP] with (R2 N)2 ECl (E=P or As; R=alkyl) granted direct access to transient amine-substituted diphospha- and arsaphospha-acrylamide analogues, (R2 N)E=P(CONR2 ) 1. Their facile formation allowed for a comprehensive reactivity study. Dimerization yielded the four-membered rings (R2 N)2 E2 P2 (CONR2 )2 , whereas in the presence of excess Na[OCP], a stepwise [2+2] cycloaddition occured, leading to the sodium salts of carboxotripnictides [(R2 N)EP2 CO(CONR2 )]- . These salts served as a reservoir of 1, either by extrusion of Na[OCP] or by reaction with the appropriate (R2 N)2 ECl, giving the [4+2]-cycloaddition products (R2 N)EP(C6 H10 )(CONR2 ) in the presence of 2,3-dimethylbutadiene. The formal conjugate addition product K[(tBuO)(R2 N)PP(CONR2 )] was obtained by reaction of Na[(R2 N)PP2 CO(CONR2 )] with tBuOK. In addition, a rare diphosphadigalletane with a ladder-type (R2 N)2 Ga2 P2 (CONR2 )2 core was isolated from the reaction of Na[OCP] with (R2 N)2 GaCl (R=alkyl). The unprecedented pnictogenyl carboxamide compounds were thoroughly characterized, including single-crystal X-ray structure determinations, and mechanisms for their formation were investigated by DFT calculations.

Simple Synthesis of Functionalized 2-Phosphanaphthalenes.

A simple synthesis of sodium 2-phosphanaphthalene-3-olate (1) based on the extrusion of N2 from phthalazine using Na[OCP] is reported. This heterocycle can be readily functionalized at the negatively charged oxygen center using a variety of electrophilic substrates. The coordination chemistry of both 1 and its neutral derivatives was explored, revealing their facile use as P-donor ligands for late-transition-metal complexes.

Metalate-Mediated Functionalization of P4 by Trapping Anionic [Cp*Fe(CO)2(η1-P4)]- with Lewis Acids.

The development of selective functionalization strategies of white phosphorus (P4) is important to avoid the current chlorinated intermediates. The use of transition metals (TMs) could lead to catalytic procedures, but these are severely hampered by the high reactivity and unpredictable nature of the tetrahedron. Herein, we report selective first steps by reacting P4 with a metal anion [Cp*Fe(CO)2]- (Cp*=C5(CH3)5), which, in the presence of bulky Lewis acids (LA; B(C6F5)3 or BPh3), leads to unique TM-substituted LA-stabilized bicyclo[1.1.0]tetraphosphabutanide anions [Cp*Fe(CO)2(η1-P4⋅LA)]-. Their P-nucleophilic site can be subsequently protonated to afford the transient LA-free neutral butterflies exo,endo- and exo,exo-Cp*Fe- (CO)2(η1-P4H), allowing controllable stepwise metalate-mediated functionalization of P4.

Functionalization of P4 through Direct P-C Bond Formation.

Research on chlorine-free conversions of P4 into organophosphorus compounds (OPCs) has a long track record, but methods that allow desirable, direct P-C bond formations have only recently emerged. These include the use of metal organyls, carbenes, carboradicals, and photochemical approaches. The versatile product scope enables the preparation of both industrially relevant organophosphorus compounds, as well as a broad range of intriguing new compound classes. Herein we provide a concise overview of recent breakthroughs and outline the acquired fundamental insights to aid future developments.

Selective [3+1] Fragmentations of P4 by "P" Transfer from a Lewis Acid Stabilized [RP4 ]- Butterfly Anion.

Two [3+1] fragmentations of the Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutanide Li[Mes*P4 ⋅ BPh3 ] (Mes*=2,4,6-tBu3 C6 H2 ) are reported. The reactions proceed by extrusion of a P1 fragment, induced by either an imidazolium salt or phenylisocyanate, with release of the transient triphosphirene Mes*P3 , which was isolated as a dimer and trapped by 1,3-cyclohexadiene as a Diels-Alder adduct. DFT quantum chemical computations were used to delineate the reaction mechanisms. These unprecedented pathways grant access to both P1 - and P3 -containing organophosphorus compounds in two simple steps from white phosphorus.

Functionalization of P4 in the coordination sphere of coinage metal cations.

Selective functionalization of white phosphorus is achieved by addition of ArLi to unique cationic coinage metal η(2)-P4 complexes. This novel approach allows controlled P-C bond formation using the bulky DmpLi (Dmp = 2,6-Mes2C6H3) and the unencumbered MesLi, giving sterically diverse doubly complexed RP4 butterfly derivatives in a single step.

Stabilization and Transfer of the Transient [Mes*P4](-) Butterfly Anion Using BPh3.

The transient bicyclo[1.1.0]tetraphosphabutane anion, generated from white phosphorus (P4) and Mes*Li (Mes*=2,4,6-tBu3C6H2), can be trapped by BPh3 in THF. This Lewis acid stabilized anion can be used as an [RP4](-) transfer agent, reacting cleanly with neutral Lewis acids (B(C6F5)3, BH3, and W(CO)5) to afford unique singly and doubly coordinated butterfly anions, and with the trityl cation to form a neutral, nonsymmetrical, all-carbon-substituted P4  derivative. This reaction path enables a simple, stepwise functionalization of white phosphorus.

Functionalization of P4 using a Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutane anion.

Reacting white phosphorus (P4 ) with sterically encumbered aryl lithium reagents (aryl=2,6-dimesitylphenyl or 2,4,6-tBu3 C6 H2 ) and B(C6 F5 )3 gives the unique, isolable Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutane anion. Subsequent alkylation of the nucleophilic site of the RP4 anion gives access to non-symmetrical disubstituted bicyclic tetraphosphorus compounds. This novel method enables PC bond formation in a controlled fashion using white phosphorus as starting material.