Das erste Distibabutadien: Synthese und Struktur vontrans-1,4-Bis(trimethylsiloxy)-1,4-bis(2,4,6-tri-tert-butylphenyl)-2,3-distibabutadien

Carbodicarbene Bismaalkene Cations: Unravelling the Complexities of Carbene versus Carbone in Heavy Pnictogen Chemistry

We report a combined experimental and theoretical study on the first examples of carbodicarbene (CDC)-stabilized bismuth complexes, which feature low-coordinate cationic bismuth centers with C=Bi multiple-bond character. Monocations [(CDC)Bi(Ph)Cl][SbF6 ] (8) and [(CDC)BiBr2 (THF)2 ][SbF6 ] (11), dications [(CDC)Bi(Ph)][SbF6 ]2 (9) and [(CDC)BiBr(THF)3 ][NTf2 ]2 (12), and trication [(CDC)2 Bi][NTf2 ]3 (13) have been synthesized via sequential halide abstractions from (CDC)Bi(Ph)Cl2 (7) and (CDC)BiBr3 (10). Notably, the dications and trication exhibit C ⇉ Bi double dative bonds and thus represent unprecedented bismaalkene cations. The synthesis of these species highlights a unique non-reductive route to C-Bi π-bonding character. The CDC-[Bi] complexes (7-13) were compared with related NHC-[Bi] complexes (1, 3-6) and show substantially different structural properties. Indeed, the CDC ligand has a remarkable influence on the overall stability of the resulting low-coordinate Bi complexes, suggesting that CDC is a superior ligand to NHC in heavy pnictogen chemistry.

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

The reaction of the phosphinidene complex [Cp*P{W(CO)₅ }₂ ] (1 a) with diphenyldiazomethane leads to [{W(CO)₅ }Cp*P=NN{W(CO)₅ }=CPh₂ ] (2). Compound 2 is a rare example of a phosphadiazadiene ligand (R-P=N-N=CR'R'') complex. At temperatures above 0 °C, 2 decomposes into the complex [{W(CO)₅ }PCp*{N(H)N=CPh₂ )₂ ] (3), among other species. The reaction of the pentelidene complexes [Cp*E{W(CO)₅ }₂ ] (E=P, As) with diazomethane (CH₂ NN) proceeds differently. For the arsinidene complex (1 b), only the arsaalkene complex 4 b [{W(CO)₅ }₂ {η^1:2 -(Cp*)As=CH₂ }] is formed. The reaction with the phosphinidene complex (1 a) results in three products, the two phosphaalkene complexes [{W(CO)₅ }₂ {η^1:2 -(R)P=CH₂ }] (4 a: R=Cp*, 5: R=H) and the triazaphosphole derivative [{W(CO)₅ }P(Cp*)-CH₂ -N{W(CO)₅ }=N-N(N=CH₂ )] (6 a). The phosphaalkene complex (4 a) and the arsaalkene complex (4 b) are not stable at room temperature and decompose to the complexes [{W(CO)₅ }₄ (CH₂ =E-E=CH₂ )] (7 a: E=P, 7 b: E=As), which are the first examples of complexes with parent 2,3-diphospha-1,3-butadiene and 2,3-diarsa-1,3-butadiene ligands.

Synthesis, structure and reactivity of ferrio-chloro-phosphanes, -arsanes and -stibanes [(CO)2(eta5-C5Me5)FePn(Cl)R] (Pn = P, As, Sb); R = tetramethylcyclopentadienyl, 2,7-di-tert-butylfluorenyl, 2,7-di-tert-butyl-9-trimethylsilylfluorenyl) as precursor to novel metallo-phosphaalkenes, -arsaalkenes, and -stibaalkenes

Reaction of one equivalent of the complexes [FeCp*(CO)2PnCl2] (Pn = P, As, Sb) with tetramethylcyclopentadienyllithium afforded compounds [FeCp*(CO)2[Pn(Cl)(C5Me4H)]]. Dehydrochlorination by means of tert-butyllithium led to decomposition. Only in the case of the phosphorus compound was evidence for the initial formation of a phosphaalkene given by 31P NMR spectroscopy. Similarly treatment of equimolar amounts of [FeCp*(CO)2PnCl2] with 2,7-di-tert-butyl-9-H-fluorenyllithium or 2,7-di-tert-butyl-9-trimethylsilylfluorenyllithium yielded the asymmetrically substituted ferriopnicogenanes [FeCp*(CO)2[Pn(Cl)-9-R-Fl*]] (Pn = P, As, Sb; R = H, Me3Si; Fl* = 2,7-di-tert-butylfluorenylidene). Dehydrohalogenation of [FeCp*(CO)2[Pn(Cl)-9-H-Fl*]] with lithium diisopropylamide resulted in the formation of the anticipated phosphaalkene [FeCp*(CO)2[P = Fl*]], whereas in the case of the arsenic and antimony derivatives the novel ferriopnicogenanes [FeCp*(CO)2[Pn(9-H-Fl*)2]] (Pn = As, Sb) were obtained as products. The new compounds were characterized by elemental analyses and spectra (IR, 1H, 13C, 29Si, 31P NMR). The molecular structures of [FeCp*(CO)2[Pn(Cl)(C5Me4H]]] (Pn = As, Sb), [FeCp*(CO)2[As(Cl)(9-Me3Si-Fl*)]] and [FeCp*(CO)2[Sb(9-H-Fl*]2] were elucidated by single X-ray diffraction analyses.