Synthesis, electrochemistry and reactivity of formato– and acetato–niobocene complexes

Abstract

The complex SiMe,),H,] I reacted with CO, to give the formato complex [Nb(q5-C,H,SiMe,),{OC(O) H-O,O'}] 2, which can alternatively be prepared from a two-electron reduction of [Nb(q5-C5H,SiMe,),CI2] 3 in the presence of formic acid. The reaction of 2 with different n-acids or heterocumulene molecules resulted in opening of the bidentate formate ligand giving rise to the monodentate formato-containing complexes [Nb(q5-C5H4SiMe,),{OC(0)H-O}L], L = CS, 4, CO 5 or 2,6-Me,C6H,NC 6. On the other hand, [Nb(q5-C,H,SiMe,),(OC(O) Me-O,O'}] 8 was prepared from either the reaction of [Nb(q5-C,H,SiMe,),CI] 7 with 1 equivalent of TI(0,CMe) or from a twoelectron reduction of 3 in the presence of acetic acid. The complex [Nb(q5-C,H,SiMe,),(MeCOCHCOMe-O,O')] 9 can also be isolated from the reaction of 7 with 1 equivalent of Tl(acac) (acac = acetylacetonate). Complex 8 reacted with oxygen to give [Nb(q5-C,H,SiMe,),O{OC(O) Me-O}] 10, and with n-acids or heterocumulenes to give products with a monodentate OC(0)Me ligand, namely [Nb(q5-C,H,SiMe,),{OC(O)Me-O}L],

New Studies on the Reactivity of Hydride-Containing Niobocene Complexes Towards Insertion and Protonation Processes

“…Complex 10 was previously prepared by some of us using different methods. [11] We have been unable to detect the η 1 -formato complex due to the difficulties involved in carrying out test reactions on an NMR-tube scale. The spectroscopic data of 10 agree with those previously described.…”

“…The spectroscopic data of 10 agree with those previously described. [11] Reactivity of [Nb(η 5 Complexes 11Ϫ13 were formed in high yield (ഠ 85%) as red solids after precipitation from Et 2 O. The 1 H NMR spectrum of 11 reveals the equivalence of the cyclopentadienyl rings, with two pseudotriplets observed at δ ϭ 5.36 and δ ϭ 5.50.…”

“…[8] In connection with our recent studies of metal-promoted activation of unsaturated molecules such as heterocumulenes, [9] carbon disulfide, [10] carbon dioxide, [11] and activated alkynes, [12] we also decided to explore the reactivity of the new hydride phosphanyl complex 3 with carbon disulfide and carbon dioxide. These reactions have permitted the isolation of dithioformato-and formatoderivatives as well as the insertion of ClPPh 2 into the NbϪH bond of the monohydride derivatives [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (H)(L)] [L ϭ PHPh 2 , CN(2,6-Me 2 C 6 H 3 ), CO], and this has allowed us to prepare new cationic Nb III species.…”

New reactivity of . Synthesis, electrosynthesis and reactivity of new carboxylato niobocene complexes

“…A few years ago, we prepared a formato niobocene complex Cp 0 2 Nbðj 2 -O; O 0 AOOCHÞ by carbon dioxide insertion into the niobium-hydrogen bond of Cp 0 2 NbH 3 . The formato complex could also be obtained from the two-electron reduction of Cp 0 2 NbCl 2 in the presence of formic acid [6]. In addition, an acetato-containing complex, namely Cp 0 2 Nbðj 2 -O; O 0 AOOCMeÞ, was also chemically and electrochemically prepared [6].…”

“…This complex constitutes an interesting example of a trihydride complex that exhibits the phenomenon of exchange coupling [1], with unusual 1 J(H,H) couplings that vary with temperature [2]. In the last 15 years we have focused our attention on the study of the reactivity of 1, e.g., with p-acid ligands to give different families of complexes Cp 0 2 NbHðLÞ; L ¼ p-acid ligand [3], in E-H (E = Si, Ge, H) 0022 6 ], M = Cu, Ag, Au to give a broad class of heterobimetallic species [5]. A few years ago, we prepared a formato niobocene complex Cp 0 2 Nbðj 2 -O; O 0 AOOCHÞ by carbon dioxide insertion into the niobium-hydrogen bond of Cp 0 2 NbH 3 .…”