RESUMEN
A set of azadiphosphiridine complexes 3a and 4b,c were synthesized in high selectivity using N-H and P-H deprotonation as key steps and RPCl2 as substrates (R = NiPr2 (a), -tBu (b), Ph (c)). While complex 3a (P-NiPr2) retained the P-W linkage of the starting material W(CO)5{Ph3CP(H)NH}, complexes 4b (P-tBu) and 4c (P-Ph) revealed that a P-to-P' haptotropic shift of the W(CO)5 group has occurred. Remarkably, complex 3a, bearing an unligated P-NiPr2 unit, displays a planar ring N geometry while 4b,c showed a pyramidal geometry of the ring nitrogen atom. Theoretical studies on the ring formation including the P-to-P' haptotropic metal shift and the factors influencing the ring nitrogen geometry are reported.
RESUMEN
A µ2-(η1,η2)-dinuclear diphosphene complex having two W(CO)5 groups with dimethyl acetylenedicarboxylate, 4-phenyl-1,2,4-triazoline-3,5-dione and diethyl azodicarboxylate was applied to P-heterocyclic synthesis, i.e., using a singlet carbene-type reactivity of a homonuclear π-system assisted by a haptotropic shift thus rendering a more nucleophilic ß phosphorus and, hence, a subsequent ring expansion.
RESUMEN
ConspectusLike singlet carbenes and silylenes, transient electrophilic terminal phosphinidene complexes enabled highly selective synthetic transformations, but the required multistep synthetic protocols precluded widespread use of these P1 building blocks. By contrast, nucleophilic M/Cl phosphinidenoid complexes can be easily accessed in one step from [M(CO)n(RPCl2)] complexes. This advantage and the mild reaction conditions opened broad synthetic applicability that enabled access to a variety of novel compounds. The chemistry will be described in this Account, including bonding and mechanistic considerations derived from high-level density functional theory calculations.In 2007, we gained the first strong evidence for the formation of these thermally labile complexes using two different synthetic approaches: P-H deprotonation and Cl/Li exchange; the latter has become the preferred method. Intense studies revealed that steric demand of the P substituents in combination with metal complexation, a donor solvent, and/or the presence of a crown ether are necessary prerequisites for the formation and especially the usability of these intermediates as novel P1 building blocks. Solution-phase NMR spectroscopy and solid-state X-ray diffraction studies revealed the bonding situation, i.e., a solvent-separated ion pair structure, and typical 31P NMR signatures of the anions. To date, we have established the following reactivity patterns for Li/Cl phosphinidenoid complexes: self-condensations (I), electrophilic and nucleophilic reactions (II), 1,1-additions (III), [2 + 1] cycloadditions (IV), ring expansions (V), and redox reactions (VI). For example, self-condensations can yield dinuclear acyclic or polycyclic diphosphane or diphosphene complexes. Their use as nucleophiles and electrophiles can be employed to access functional phosphane ligands with mixed substitution patterns. 1,1-Addition reactions were a puzzling discovery because the resulting products resembled classical P-C π-bond structures but the bonding was more of a donor-to-phosphorus adduct with significant differences in bonding parameters. Into the same category and also surprising fall formal E-H insertion reactions leading to 1,1'-bifunctional phosphane complexes. To date, the most important synthetic impact was achieved in the chemistry of strained P-heterocyclic ligands such as oxaphosphiranes and azaphosphiridines, obtained via [2 + 1] cycloadditions of the title compounds with carbonyls and imines, respectively. Ring expansions have been shown to yield 1,2-oxaphosphetanes and 1,2-thiaphosphetanes, and because of the pool of industrially important epoxides, this provides straightforward and affordable access to these novel P-heterocyclic ligands, which also promise to be of interest in catalytic applications. Recent developments describe redox transformations of Li/Cl phosphinidenoid complexes into new reactive intermediates such as complexes with open-shell P-functional phosphanyl ligands via oxidative single electron transfer reactions or into terminal electrophilic phosphinidene complexes via chloride elimination. The latter is clearly restricted to P-amino derivatives because of their enhanced π-donation capability, as evidenced in a recent study on umpolung of these reactive intermediates. While our efforts to expand M/X phosphinidenoid complex chemistry are ongoing, we want to emphasize that the development of new reactive intermediates not only improves our understanding of bonding and reactivity but also opens new perspectives in organoelement chemistry.
RESUMEN
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.
RESUMEN
Complexes [Fe(CO)4(RPCl2)] (2) (a: R = CPh3, b: R = tBu) were used to generate the first examples of phosphinidenoid iron(0) complexes [Li(12-crown-4)(solv)n][Fe(CO)4(RPCl] (3a,b), characterized by NMR spectroscopy. The bonding situation of 3 was analyzed for a P-Me model complex using DFT calculations. Complex 3a (R = CPh3) reacted with H2O and MeOH to give selectively O-H bond insertion products 5 and 7; for the case of H2O, a multistep electrophilic reaction is supported by detailed DFT calculations. Clear-cut evidence for an unprecedented electrophilic reactivity of 3a was obtained as a reaction with MeLi led to P-chloro substitution. The intermediately formed phosphanido complex [Fe(CO)4(Ph3CPMe)] (8) was quenched with HCl or MeOTf to furnish neutral iron(0) complexes 9 and 10.
RESUMEN
Synthesis of 1,1'-bifunctional aminophosphane complexes 3 a-e was achieved by the reaction of Li/Cl phosphinidenoid complex 2 with various primary amines (R=Me, iPr, tBu, Cy, Ph). Deprotonation of complex 3 a (R=Me) with potassium hexamethyldisilazide yielded a mixture of K/NHMe phosphinidenoid complex 4 a and potassium phosphanylamido complex 4 a'. Treatment of complex 3 c (R=tBu) and e (R=Ph) with KHMDS afforded the first examples of K/NHR phosphinidenoid complexes 4 c and e. The reaction of complex 3 c with 2 molar equivalents of KHMDS followed by PhPCl2 afforded complexes 5 c,c', which possess a P2 N-ring ligand. All complexes were characterized by NMR, IR, MS, and microanalysis, and additionally, complexes 3 b-e and 5 c' were scrutinized by single-crystal X-ray crystallography.
RESUMEN
Two new catalytic systems for hydrogen-atom transfer (HAT) catalysis involving the N-H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis.