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The nitrido‐ate complex [(PN)2Ti(N){μ2‐K(OEt2)}]2 (1) reductively couples CO and isocyanides in the presence of DME or cryptand, to form rare, five‐coordinate TiII complexes having a linear cumulene motif, [K(L)][(PN)2Ti(NCE)] (E = O, L = Kryptofix222, (2); E = NAd, L = 3 DME, (3); E = NtBu, L = 3 DME, (4); E = NAd, L = Kryptofix222, (5)). Oxidation of 2‐5 with [Fc][OTf] afforded an isostructural TiIII center containing a neutral cumulene [(PN)2Ti(NCE)] (E = O, (6); E = NAd (7), NtBu (8)). Moreover, 1e‐ reduction of 6 and 7 in the presence of cryptand cleanly reformed corresponding discrete TiII complexes 2 and 5, which were further characterized by solution magnetization measurements and high‐ frequency and ‐field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with [Fc*][B(C6F5)4] resulted in a ligand disproportionated TiIV complex having transoid carbodiimides, [(PN)2Ti(NCNAd)2] (9). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as TiII→TiIII→TiIV and increasing order of p‐donation as TiII→TiIII→TiIV, thus displaying more covalency in TiIII species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N‐atom to π‐acids.

 

We show in this work how lithium tellurolate Li(X)_nTeCH₂SiMe₃(X = THF,n= 1, 1; X = 12-crown-4,n= 2, 2), can serve as an effective Te-atom transfer reagent to all group 5 transition metal halide precursors irrespective of their oxidation state.

 

The complex [(BDI)VCl(N{SiMe3}2)] (1) (BDI– = [ArNC(CH3)]2CH, Ar = 2,6-iPr2C6H3), a precursor readily prepared from metathesis of [(BDI)VCl2] and Na[N{SiMe3}2], can be reduced with Na/NaCl in the presence of white P4 to form a dinuclear species containing two VIII centers bridged by a tricyclic [P6]2– scaffold, namely, [(BDI)V(N{SiMe3}2)]2(μ-η1:η1-P6) (2). Coordination of [P6]2– involves a unique chairlike μ-η1:η1 binding mode with a contiguous tricyclic hexaphosphorus unit bridging across the two V centers. Complexes 1 and 2 have been structurally characterized, and a pathway toward the formation of the chairlike tricyclic [P6]2– scaffold in 2 is proposed. 

Complex (PNP)NbCl 2 (N[ t Bu]Ar) (1) (PNP − = N[2-P i Pr 2 -4-methylphenyl] 2 ; Ar = 3,5-Me 2 C 6 H 3 ) reacts with one equiv. of NaN 3 to form a mixture of (PNPN)NbCl 2 (N[ t Bu]Ar) (2) and (PNP)NbN(N[ t Bu]Ar) (3), both of which have been spectroscopically and crystallographically characterized, including 15 N isotopic labelling studies. Complex 3 represents the first structurally characterized example of a neutral and mononuclear Nb nitride. Independent studies established 3 to form via two-electron reduction of 2, whereas oxidation of 3 by two-electrons reversed the process. Computational studies suggest the transmetallation step to produce the intermediate [(PNP)NbCl(N 3 )(N[ t Bu]Ar)] (A) which extrudes N 2 to form the phosphinimide [(PNPN)NbCl(N[ t Bu]Ar)] (B) followed by disproportionation to 2 and low-valent [(PNPN)Nb(N[ t Bu]Ar)] (C). The latter then undergoes intramolecular N-atom transfer to form the nitride moiety in 3. 

Decarbonylation along with P‐atom transfer from the phosphaethynolate anion, PCO⁻, to the Nb^IVcomplex [(PNP)NbCl₂(N^tBuAr)] (1) (PNP=N[2‐PⁱPr₂‐4‐methylphenyl]₂⁻; Ar=3,5‐Me₂C₆H₃) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(N^tBuAr)] (2). Reduction of2with CoCp*₂cleaves the P−P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(N^tBuAr)] (3). Theoretical studies have been used to understand both the coupling of the P‐atom and the reductive cleavage of the P−P bond. Reaction of3with a two‐electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P−P coupled ligand, namely [(PNPP)Nb=S(N^tBuAr)] (4).

 

Decarbonylation along with P‐atom transfer from the phosphaethynolate anion, PCO⁻, to the Nb^IVcomplex [(PNP)NbCl₂(N^tBuAr)] (1) (PNP=N[2‐PⁱPr₂‐4‐methylphenyl]₂⁻; Ar=3,5‐Me₂C₆H₃) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(N^tBuAr)] (2). Reduction of2with CoCp*₂cleaves the P−P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(N^tBuAr)] (3). Theoretical studies have been used to understand both the coupling of the P‐atom and the reductive cleavage of the P−P bond. Reaction of3with a two‐electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P−P coupled ligand, namely [(PNPP)Nb=S(N^tBuAr)] (4).