M/X Phosphinidenoid Metal Complex Chemistry

Abstract

Conspectus Like 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 te...

Regioselective N- versus P-Deprotonation of Aminophosphane Tungsten(0) Complexes

“…The 31 P resonance signals of M-5b are 20 ppm downfield-shifted in comparison to 3b, in general, which is in accordance to previously observed M/N(H)R phosphinidenoid complexes [15][16][17]. In addition, the 1 J W,P coupling constant has a characteristically small value [12][13][14][15][16][17][18][19]. Presumably related to the decomposition of crown ethers in basic media at ambient temperatures, M-5b turned out to be thermally unstable and could not be further characterized, in contrast to previous studies, which even allowed for the isolation of a K/N(H)R phosphinidenoid complex [16,17], but not for the isolation of the corresponding amide complex.…”

“…The alternative use of Li/Cl phosphinidenoid complexes in the formation of aminophosphane complexes of type IV was first reported by us in 2012, using the formal N-H insertion [12,13]. The broader scope of this E-H insertion chemistry was reported more recently [14][15][16][17] including an overview of formal N-H insertion of Li/X phosphinidenoid complexes [18], adding first examples of V, but focusing on sterically demanding substituents, such as triphenylmethyl and bis(trimethylsilyl)methyl, together with W(CO) 5 and Fe(CO) 4 metal fragments [12][13][14][15][16][17][18][19]. Studies on the chemistry of 1,1 -bifunctional aminophosphane complexes V included reactions targeting the P-N bond with hydrogen halides [7] and the P-H bond via deprotonation [12][13][14][15][16][17][18].…”

Understanding the Nature and Properties of Hydrogen–Hydrogen Bonds: The Stability of a Bulky Phosphatetrahedrane as a Case Study

“…Related phosphorus anions have been referred to as phosphinidenoids, in analogy to carbenoids . Bulky transition-metal-stabilized phosphinidenoids have been isolated and characterized; however, [2 + 1]-cycloaddition reactivity of these species appears to be limited to heteronuclear π-systems, such as ketones and imines. , …”

“…74 Bulky transition-metal-stabilized phosphinidenoids have been isolated and characterized; however, [2 + 1]-cycloaddition reactivity of these species appears to be limited to heteronuclear π-systems, such as ketones and imines. 75,76 Quantum chemical calculations were employed to elucidate the mechanism of ( t BuC) 3 P formation. Geometries were optimized at the ma-def2-TZVP(-f)/B3LYP-D3BJ, CPCM-(THF) level of theory, and the Gibbs free enthalpies (T = 298.15 K) were obtained using single-point energies calculated at the DLPNO-CCSD(T)/aug-cc-pVDZ, CPCM(THF) level of theory.…”

Dearomatization [4+2] Cycloaddition of Nonactivated Benzene Derivatives

“…The chemistry of low-coordinate phosphorus species is different from the chemistry of classic tricoordinate and tetracoordinate ones . The 1,4-addition of the phosphinidene complex to an active bent benzene ring was achieved by Lammertsma and Bickelhaupt .…”