Reactivity of Terminal Electrophilic Phosphinidene Complexes:  Synthesis of the First Rhenium Phosphinidene, [Re(CO)₅(η¹-PNⁱPr₂)][AlCl₄], and Novel Reactions with Azobenzene

Abstract

The first terminal rhenium phosphinidene complex, [Re(CO) 5 (η 1 -PN i Pr 2 )][AlCl 4 ], has been synthesized by chloride abstraction from [Re(CO) 5 {P(Cl)-(N i Pr 2 )}]. The electrophilic character of the terminal phosphinidene ligand is demonstrated by phosphine addition at the unsaturated phosphorus center and by novel reactions with azobenzene, PhNdNPh, which generate, via C-H activation and P-N and P-C bond formation, coordinated benzodiazaphosphole ligands. The cations [Re(CO) 5 P(PPh 3 )N i Pr 2 ] + and [Re(CO) 5 -{P(PhNNHC 6 H 4 )N i Pr 2 }] + have been crystallographically characterized as their AlCl 4salts. The corresponding late-metal terminal phosphinidene complexes [Co(CO) 3 -(PR 3 )(η 1 -PN i Pr 2 )][AlCl 4 ] (R ) Ph, Et) also afford coordinated benzodiazaphospholes via reaction with PhNd NPh.

Formation of phosphorus heterocycles using a cationic electrophilic phosphinidene complex

“…This reactivity is the same as that reported for stable cationic rhenium and cobalt phosphinidenes [16], but contrasts with that of neutral transient tungsten phosphinidenes, which simply insert into an ortho CeH bond [25]. Compound 10 was characterized spectroscopically, and the spectral data are consistent with the published data for rhenium and cobalt benzodiazoephosphole complexes.…”

“…Since then a wide range of stable electrophilic terminal phosphinidene complexes have been synthesized [13e16]. The reactivity of stable, cationic phosphinidene complexes has not been as well studied as that of the neutral transient species, but examples of nucleophilic addition [17], bond activation [18], and cycloaddition reactions [13,16] have been described.…”

Synthesis and Structural Characterization of the First Thermally Stable, Neutral, and Electrophilic Phosphinidene Complexes of Vanadium

“…The chemistry of these two classes of molecules is now being intensively explored. 4,21,22,[27][28][29] (ii) The presence and nature of metal-main group element multiple bonding (MdP, MtP) in these complexes is of theoretical and reactivity interest. 30 (iii) In terminal M-PR molecules, the phosphorus atom is in a low oxidation state (þ1) and coordination number (2), providing an opportunity to explore fundamentally different chemistry at a P(I) center.…”

“…38 Over the past few years we have isolated a series of cationic, terminal complexes including the remaining member [Cp*Cr(CO) 3 -{PN 21,[23][24][25]34 These molecules, all of which have been structurally characterized, display several important features. They are thermally stable, despite in some notable cases, such as the Re and Co compounds, the lack of sterically encumbered substituents on the metal or phosphorus ligand.…”

Direct Conversion from Terminal Borylene into Terminal Phosphinidene

“…[2] Since the first structurally authenticated example by Lappert in 1987, [3] the library of stable transition-metal terminal phosphinidene complexes containing metal-phosphorus multiple bonds and dicoordinate phosphorus atoms has been growing steadily.M irroring alkylidene chemistry,t ransition-metal terminal phosphinidene complexes (M = PR) fall between two extreme bonding descriptions:t he high-oxidation-state nucleophilic phosphinidenes (cf.S chrock carbenes) and the low-oxidation-state electrophilic phosphinidenes (cf.F ischer carbenes). [4] Although the synthesis of the latter class was previously considered more challenging,with the carbonyl-ligated metal phosphinidenes of the form [(OC) n M = PR] yet to be structurally characterized, terminal phosphinidene complexes can be achieved now through 1) condensation of lithium phosphides with metal halides, [5] 2) salt elimination between metal anions and phosphine halides, [3,6] 3) halogen/hydrogen abstraction [7] or migration, [8] 4) addition of phosphides to alkylidene with concurrent hydrogen migration, [9] 5) dehydrohalogenation, [5b,10] 6) P=Cb ond cleavage of ap hosphaketene, [11] or 7) oxidation/deprotonation. [12] Although structurally characterized terminal phosphinidene complexes of the form [L n M=P-R] are available for most of the d-block metals,t here are few reports of isolated Group 7p hosphinidenes.…”