Chemistry of the Oxophosphinidene Ligand. 1. Electronic Structure of the Anionic Complexes [MCp{P(O)R*}(CO)₂]⁻(M = Mo, W; R* = 2,4,6-C₆H₂^tBu₃) and Their Reactions with H⁺and C-Based Electrophiles.

Abstract

The anionic phosphide-bridged complexes (H-DBU)[M(2)Cp(2)(μ-PHR*)(CO)(4)] (M = Mo, W; R* = 2,4,6-C(6)H(2)(t)Bu(3); Cp = η(5)-C(5)H(5), DBU = 1,8-diazabicyclo [5.4.0] undec-7-ene) react with molecular oxygen to give the corresponding oxophosphinidene complexes (H-DBU)[MCp{P(O)R*}(CO)(2)] as major products (Mo-P = 2.239(1) Å for the Mo complex). The latter anionic complexes are protonated by HBF(4)·OEt(2) to give the hydroxyphosphide derivatives [MCp{P(OH)R*}(CO)(2)]. In the presence of excess acid, the molybdenum complex yields the fluorophosphide complex [MoCp(PFR*)(CO)(2)] (Mo-P = 2.204(1) Å), while the tungsten compound reacts with excess HCl to give an unstable chlorophosphine complex [WCpCl(PHClR*)(CO)(2)] which is rapidly hydrolyzed to give [WCpCl{PH(OH)R*}(CO)(2)], having a complexed arylphosphinous acid (Mo-P = 2.460(2) Å). The molybdenum anion reacts with strong C-based electrophiles such as [Me(3)O]BF(4), Et(2)SO(4), C(2)H(3)C(O)Cl, and PhC(O)Cl to give the corresponding alkoxyphosphide derivatives [MoCp{P(OR)R*}(CO)(2)] (R = Me, Et, COC(2)H(3), COPh; Mo-P = 2.197(2) Å for the benzoyl compound), as a result of the attack of the electrophile at the O atom of the oxophosphinidene ligand. In contrast, the reactions with milder alkylating reagents such as the alkyl halides MeI, EtI, C(3)H(5)Br, and C(3)H(3)Br give selectively the corresponding κ(2)-phosphinite complexes [MoCp{κ(2)-OP(R)R*}(CO)(2)] [R = Me, Et, C(3)H(5), C(3)H(3); Mo-P = 2.3733(5) Å for the allyl compound] as a result of the attack of the electrophile at the P atom of the oxophosphinidene ligand. According to density functional theory (DFT) calculations, the oxygen atom of the phosphinidene ligand bears the highest negative charge in the molybdenum anion, while the highest occupied molecular orbital (HOMO) of this complex has substantial Mo-P π bonding character. Thus, it is concluded that the phosphinite complexes are formed under conditions of orbital control, while charge-controlled reactions tend to give alkoxyphosphide derivatives.

Nucleophilic behaviour of dioxo- and thiooxophosphorane complexes [MoCp(CO)2{E,P-EP(O)(2,4,6-C6H2tBu3)}]−(E = O, S)

“…2.50 Å, consistent with single Mo-P bonds, while the terminal PvO bond lengths of 1.51 Å have remained almost unperturbed (cf. 1.518 Å in 1), 5 and consistent with a considerable multiple bond character, close to a formal order of two. We note that the computed P-O lengths for free P(O)R* (1.501 Å), 5 and MePO 2 (1.461 Å), 2 are only slightly shorter than the above figures.…”

“…1.518 Å in 1), 5 and consistent with a considerable multiple bond character, close to a formal order of two. We note that the computed P-O lengths for free P(O)R* (1.501 Å), 5 and MePO 2 (1.461 Å), 2 are only slightly shorter than the above figures. In contrast, the P-O length for the Mo-bound oxygen in 2 is substantially longer, as expected for an interaction approaching the single-bond character.…”

“…A final structural feature deserving comment is the distorted trigonal pyramidal environment around the P atom, derived from the fact that this atom remains placed almost in the same plane as the Mo, O3 and C11 atoms (Σ(X-P-Y) = 354°). Although no S,P-bound phosphonothiolate complex other than 6 has been structurally characterized, we note that this local environment is also present in related O,P-bound phosphinite and phosphonite complexes, 4,5 and also in the S,P-bound thiophosphinite (or phosphinothiolate) complexes [WCp(SPCl t Bu)(CO) 2 ], 16 [WCp{SPMeN(SiMe 3 ) 2 }(CO) 2 ] 17 and [Mo(C 6 H 7 )(SPMe 2 )(CO) 2 ]. 18 Spectroscopic data in solution for the phosphonothiolate complexes 6 and 7 (Table 1 and the Experimental section) are fully consistent with their asymmetric solid-state structures and deserve no particular comment.…”

“…Thus, the latter reacts with S 8 to give the corresponding tungsten derivative (H-DBU)-[WCp(CO) 2 {S,P-SP(O)R*}] (3′) in good yield. The formation of the above compounds can be viewed as resulting from addition of a chalcogen atom (E) to the MovP bond via the HOMO of the starting oxophosphinidene complex, which has π(Mo-P) bonding character and displays lobes oriented perpendicular to the Mo-P-O plane, 5 and is thus expected to leave the newly incorporated atom E nearly perpendicular to that plane (Scheme 1), in agreement with the calculations on 2 and 3 described below. Spectroscopic data in solution for compounds 2, 3 and 3′ (Table 1 and the Experimental section) are fully consistent with the structure proposed for the corresponding anions.…”

Aminotroponiminate and Aminotroponate Complexes of Group 15 (P, As) Elements: Synthesis, X‐ray Diffraction Analysis and Reactivity

“…The tungsten atom is octahedrally coordinated with an almost linear C ax –W–P angle of 173.33(15)°. The bond length of P–W [2.4584(9) Å] lies between the P–W lengths in [W(PCl 3 )(CO) 5 ] [2.378(2) Å]25 and [W(PMe 3 )(CO) 5 ] [2.516(2) Å]25 and is nearly identical to the P–W bond length [2.460(2) Å] of the hydroxyphosphide complex [WClCp{PH(OH)R}(CO) 2 ] (R = 2,4,6‐C 6 H 2 t Bu 3 ) 26…”