Reaction of Pentelidene Complexes with Diazoalkanes: Stabilization of Parent 2,3-Dipnictabutadienes

A Ruthenophosphanorcaradiene as a Synthon for an Ambiphilic Metallophosphinidene

Reaction of the ruthenium carbene complex Cp*(IPr)RuCl (1) (IPr = 1,3-bis(Dipp)imidazol-2-ylidene; Dipp = 2,6-diisopropylphenyl) with sodium phosphaethynolate (NaOCP) led to intramolecular dearomatization of one of the Dipp substituents on the Ru-bound carbene to afford a Ru-bound phosphanorcaradiene, 2. Computations by DFT reveal a transition state characterized by a concerted process whereby CO migrates to the Ru center as the P atom adds to the π system of the aryl group. The phosphanorcaradiene possesses ambiphilic properties and reacts with both nucleophilic and electrophilic substrates, resulting in rearomatization of the ligand aryl group with net P atom transfer to give several unusual metal-bound, P-containing main-group moieties. These new complexes include a metallo-1-phospha-3-azaallene (Ru─P═C═NR), a metalloiminophosphanide (Ru─P═N─R), and a metallophosphaformazan (Ru─P(═N─N═CPh2)2). Reaction of 2 with the carbene 2,3,4,5-tetramethylimidazol-2-ylidene (IMe4) produced the corresponding phosphaalkene DippP═IMe4.

Syntheses and Structures of 5-Membered Heterocycles Featuring 1,2-Diphospha-1,3-Butadiene and Its Radical Anion

LGa(P2 OC)cAAC 2 features a 1,2-diphospha-1,3-butadiene unit with a delocalized π-type HOMO and a π*-type LUMO according to DFT calculations. [LGa(P2 OC)cAAC][K(DB-18-c-6)] 3[K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene radical anion 3⋅- was isolated from the reaction of 2 with KC8 and dibenzo-18-crown-6. 3 reacted with [Fc][B(C6 F5 )4 ] (Fc=ferrocenium) to 2 and with TEMPO to [L-H Ga(P2 OC)cAAC][K(DB-18-c-6)] 4[K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene anion 4- . The solid state structures of 2, 3K(DB-18-c-6], and 4[K(DB-18-c-6] were determined by single crystal X-ray diffraction (sc-XRD).

P–C, P–N, and M–N Bond Formation Processes in Reactions of Heterometallic Phosphinidene-Bridged MoMn and MoRe Complexes with Diazoalkanes and Organic Azides to Build Three- to Five-Membered Phosphametallacycles

Reactions of the heterometallic MoRe complex [MoReCp(μ-PR*)(CO)₆] and its MoMn analogue with some small molecules having N–N multiple bonds, such as diazoalkanes and organic azides, were investigated (R* = 2,4,6-C₆H₂^tBu₃). Reactions with excess ethyl diazoacetate proceeded slowly and with concomitant denitrogenation to give complexes [MoMCp(μ-η²_P,C:κ²_P,O-PR*CHCO₂Et)(CO)₅], which display a bridging phosphaalkene ligand in a novel μ-η²:κ² coordination mode, while reactions with other diazoalkanes resulted only in the decomposition of the organic reagent. The MoRe complex reacted with benzyl- or p-tolyl azide at room temperature to give the green complexes [MoReCp(μ-η²_P,N:κ_P,N′²-PR*N₃R)(CO)₆] [R = Bn, p-tol], which display bridging phosphatriazadiene ligands in a novel 6-electron donor coordination mode as a result of a formal [2 + 1] cycloaddition of the terminal N atom of the azide to the Mo–P double bond of the parent complex, followed by coordination of the distal NR nitrogen to the rhenium center. Denitrogenation was only observed for the p-tolyl azide derivative, which upon heating at 333 K yielded [MoReCp{μ-κ_P:κ_N-PR*N(p-tol)}(CO)₆], a molecule displaying a bridging phosphaimine ligand in a rare κ_P:κ_N coordination mode. Analogous reactions of the MoMn phosphinidene complex proceeded similarly at 273 K to give the phosphatriazadiene-bridged derivatives [MoMnCp(μ-η²_P,N:κ²_P,N′-PR*N₃R)(CO)₆], but these were thermally unstable and degraded at room temperature to give the mononuclear triazenylphosphanyl complexes [Mn²(κ_P,N-PR*NHNNR)(CO)₃] as major products, along with small amounts of the phosphaimine-bridged complex [MoMnCp{μ-κ_P:κ_N-PR*N(p-tol)}(CO)₆] in the case of the p-tolyl azide derivative. The structure of the new complexes was analyzed in light of spectroscopic data and single-crystal diffraction studies on selected examples of each type of complex.

Reactions of [MoMCp(μ-PR)(CO)₆] (M = Mn, Re) with N₂CHCO₂Et involved denitrogenation and decarbonylation to give derivatives with a phosphaalkene ligand in a novel μ-κ²:η² coordination mode. However, reactions with organic azides involved [2 + 1] cycloaddition of the terminal nitrogen to the Mo−P double bond of the parent complex and coordination of the distal NR nitrogen without decarbonylation to give phosphatriazadiene derivatives, which evolved differently depending on R and M, to give either phosphaimine or triazenylphosphanyl derivatives.

Isolation of singlet carbene derived 2-phospha-1,3-butadienes and their sequential one-electron oxidation to radical cations and dications

A synthetic strategy for the 2-phospha-1,3-butadiene derivatives [{(IPr)C(Ph)}P(cAAC^Me)] (3a) and [{(IPr)C(Ph)}P(cAAC^Cy)] (3b) (IPr = C{(NDipp)CH}₂, Dipp = 2,6-iPr₂C₆H₃; cAAC^Me = C{(NDipp)CMe₂CH₂CMe₂}; cAAC^Cy = C{(NDipp)CMe₂CH₂C(Cy)}, Cy = cyclohexyl) containing a C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C–PC framework has been established. Compounds 3a and 3b have a remarkably small HOMO–LUMO energy gap (3a: 5.09; 3b: 5.05 eV) with a very high-lying HOMO (−4.95 eV for each). Consequently, 3a and 3b readily undergo one-electron oxidation with the mild oxidizing agent GaCl₃ to afford radical cations [{(IPr)C(Ph)}P(cAAC^R)]GaCl₄ (R = Me 4a, Cy 4b) as crystalline solids. The main UV-vis absorption band for 4a and 4b is red-shifted with respect to that of 3a and 3b, which is associated with the SOMO related transitions. The EPR spectra of compounds 4a and 4b each exhibit a doublet due to coupling of the unpaired electron with the ³¹P nucleus. Further one-electron removal from the radical cations 4a and 4b is also feasible with GaCl₃, affording the dications [{(IPr)C(Ph)}P(cAAC^R)](GaCl₄)₂ (R = Me 5a, Cy 5b) as yellow crystals. The molecular structures of compounds 3–5 have been determined by X-ray diffraction and analyzed by DFT calculations.

The 2-phospha-1,3-butadiene derivatives 3 are readily accessible by reduction of 2 with Mg. Sequential one-electron oxidation of 3 with GaCl₃ leads to the formation of radical cations 4 and dications 5 as crystalline solids.

Isolation of singlet carbene derived 2-arsa-1,3-butadiene radical cations and dications

2-Arsa-1,3-butadienes (L)As(cAACR) (L = PhC[double bond, length as m-dash]C{(NDipp)CH}2, Dipp = 2,6-iPr2C6H3; cAACR = C{(NDipp)CMe2CH2C(R)}, R = Me22a, R = cyclohexyl (Cy) 2b) and the corresponding radical cations [(L)As(cAACR)]GaCl4 (R = Me23a, Cy 3b) and dications [(L)As(cAACR)](GaCl4)2 (R = Me 4a, Cy 4b) featuring a C[double bond, length as m-dash]C-As[double bond, length as m-dash]C π-conjugated framework are reported.

Ring Expansions of Nonpolar Polyphosphorus Rings

The reaction of the phosphinidene complex [Cp*P{W(CO)₅ }₂ ] (1 a) (Cp*=C₅ Me₅ ) with the anionic cyclo-P_n ligand complex [(η³ -P₃ )Nb(ODipp)₃ ]^- (2, Dipp=2,6-diisopropylphenyl) resulted in the formation of [{W(CO)₅ }₂ {μ₃ ,η^3:1:1 -P₄ Cp*}Nb(ODipp)₃ ]^- (3), which represents an unprecedented example of a ring expansion of a polyphosphorus-ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO)₅ }₂ ] (E=P: 1 a, As: 1 b) with the neutral complex [Cp'''Co(η⁴ -P₄ )] (Cp'''=1,2,4-tBu₃ C₅ H₂ ) led to a cyclo-P₄ E ring (E=P, As) through the insertion of the pentel atom into the cyclo-P₄ ligand. Starting from 1 a, the two isomers [Cp'''Co(μ₃ ,η^4:1:1 -P₅ Cp*){W(CO)₅ }₂ ] (5 a,b), and from 1 b, the three isomers [Cp'''Co(μ₃ ,η^4:1:1 -AsP₄ Cp*){W(CO)₅ }₂ ] (6 a-c) with unprecedented cyclo-P₄ E ligands (E=P, As) were isolated. The complexes 6 a-c represent unique examples of ring expansions which lead to new mixed five-membered cyclo-P₄ As ligands. The possible reaction pathways for the formation of 5 a,b and 6 a-c were investigated by a combination of temperature-dependent ³¹ P{¹ H} NMR studies and DFT calculations.

Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Muonium (Mu), an H atom analogue, is employed to probe the addition of free radicals to the P=C bond of a phosphaalkene. Specifically, two unprecedented muoniated free radicals, MesP^. -CMu(Me)₂ (1 a, minor product) and MesPMu-C^. Me₂ (1 b, major product), were detected by muon spin spectroscopy (μSR) when a solution of MesP=CMe₂ (1: Mes=2,4,6-trimethylphenyl) was exposed to a beam of positive muons (μ⁺ ). The μ⁺ serves as a source of Mu (that is, Mu=μ⁺ +e^- ). To confirm the identity of the major product 1 b, its spectral features were compared to its isotopologue, MesPH-C^. (Me)CH₂ Mu (2 a). Conveniently, 2 a is the sole product of the reaction of MesPH(CMe=CH₂ ) (2) with Mu. For all observed radicals, muon, proton, and phosphorus hyperfine coupling constants were determined by μSR and compared to DFT-calculated values.

Versatile Coordination Modes of Triphospha-1,4-pentadiene-2,4-diamine

1,3,5-Triphospha-1,4-pentadiene-2,4-diamine reacts with [M(CO)₄L] (M = Mo, L = nbd (norbornadiene); M = W, L = 2 CH₃CN) to give the chelate complexes [M(CO)₄(PMes{C(NHCy)PMes}₂-κ P¹ ,P³)]. In contrast, an unusual intramolecular rearrangement occurred with [Cu(CH₃CN)₄]PF₆ leading to the dimeric copper(I) complex [Cu(CNCy){PHMesPMesC(NHCy)PMes-κ P¹ ,P³}]₂(PF₆)₂. The mechanism of the rearrangement was supported by quantum-mechanical calculations. The transition-metal complexes were characterized by multinuclear NMR spectroscopy, mass spectrometry, infrared spectroscopy, and X-ray crystallography.