124618-92-4Relevant articles and documents
Base-Induced Alkyne Cleavage in W(II) Complexes - a New Way to Low Valent Carbyne Complexes from W(CO)6
Filippou, Alexander Constantin,Voelkl, Christian,Gruenleitner, Walter,Kiprof, Paul
, p. 351 - 368 (2007/10/02)
A new entry to low-valent, carbonyl-free tungsten phenylcarbyne complexes has been developed from W(CO)6 via tungsten(II) alkyne complexes.The first step includes thermal decarbonylation of W(CO)6 to fac-W(CO)3(MeCN)3 and subsequent substitution of the acetonitrile ligands by EtNC or t-BuNC to give fac-W(CO)3(EtNC)3 (1a) or fac-W(CO)3(t-BuNC)3 (1b) in almost quantitative yield.Advantages of this indirect synthesis of 1a and 1b from W(CO)6 are discussed in comparison to the previously described, CoCl2 catalyzed transformation of W(CO)6 with RNC to fac-W(CO)3(RNC)3.Compounds 1a and 1b are then quantitatively converted with Br2 to W(CO)2(EtNC)3(Br)2 (2a) and W(CO)2(t-BuNC)3(Br)2 (2b). 2a and 2b react subsequently with PhCCBr to give upon elimination of both CO ligands the carbonyl-free compounds W(EtNC)3(ν2-PhCCBr)(Br)2 (3a) and W(t-BuNC)3(ν2-PhCCBr)(Br)2 (3b) in good yield. 3a and 3b represent rare examples of complexes containing 1-haloalkyne ligand.They are susceptible to nucleophilic attack at this ligand.Thus reaction of 3a and 3b with t-BuNH2 or Et2NH gives the 1-aminoalkyne complexes W(EtNC)32-PhCCNH(t-Bu)>(Br)2 (4a), W(t-BuNC)32-PhCCNH(t-Bu)>(Br)2 (4b) and W(t-BuNC)3(ν2-PhCCNEt2)(Br)2 (4c) in good yields.Finally, a base-induced cleavage of the alkyne ligand is achieved in 4a and 4b using LiPh and gives the carbyne complexes mer,trans-Br(t-BuNC)(EtNC)3WCPh (5a) and trans-Br(t-BuNC)4WCPh (5b).This decoupling reaction is the first example of an alkyne-bond cleavage to C1-fragments at a single transition metal center and the key step in the new synthetic procedure to 5a and 5b from W(CO)6.Complex 5b has been previously prepared from W(CO)6 by the classical Fischer route via the carbonyl containing carbyne complex trans-Br(CO)4WCPh and has been shown to undergo the reverse of the decoupling reaction i. e. an HBr-induced coupling of a tert-butylisocyanide with the phenylcarbyne ligand to form 4b.The compositions and structures of the complexes 1a-5b have been determined by total elemental analyses, IR, 1H NMR, 13C NMR and mass spectra.The spectroscopic results indicate a substantial bond delocalization in the 1-aminoalkyne complexes 4a-4c and a hindered rotation of the diethylamino group in the alkyne ligand of 4c.The barrier of this rotation is calculated to be ca. 14.7 kcal/mol and compared with previously reported diethylaminoalkyne complexes.An X-ray crystallographic study of 5b has been carried out.The compound crystallizes in the monoclinic space group P21.The unit cell contain two molecules of 5b, which have a distorted octahedral coordination geometry with a trans-arrangement of the bromo and the phenylcarbyne ligand.The four isocyanide ligands are slightly bent out of the equatorial plane towards the bromo ligands.Striking features of the structure are the shortest WCcarbyne and the longest W-Br bond lengths known for low valent tungsten aryl- and alkylcarbyne complexes indicating a ...
