Two Types of σ‐Allenyl Complexes from Reactions of Silylenes and Germylenes with Chromium Fischer Alkynyl(alkoxy)carbenes

Abstract

The reactivity of amidinatotetrylenes of the type E(tBu2bzm)R1 (E=Si, Ge; tBu2bzm=N,N′‐bis(tertbutyl)benzamidinate; R1=alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C2R2}(CO)5] (R2=Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C2 atom (γ‐attack), which leads to σ‐allenyl complexes in which the original Ccarbene atom maintains its attachment to the Cr(CO)5 and OEt groups (compounds 3boldE-boldR1-boldR2 ), and (b) attack of the amidinatotetrylene to the Ccarbene atom (α‐attack), which ends in σ‐allenyl complexes in which the original Ccarbene atom is not attached to the metal atom and has been inserted into an E−N bond of the amidinatotetrylene forming an E‐C‐N‐C‐N five‐membered ring (compounds 4boldE-boldR1-boldR2 ). It has been found that compounds 3boldE-boldR1-boldR2 are thermodynamically less stable than their corresponding 4boldE-boldR1-boldR2 isomers and that some of the former (E=Ge; R1=CH2SiMe3) can be transformed into the latter upon heating. At high temperatures (>70 °C) the reactions involving bulky amidinatotetrylenes (R1=Mes, tBu) end in the carbene‐substitution products [Cr{E(tBu2bzm)R1}(CO)5].

Mesityl(amidinato)tetrylenes as ligands in iridium(i) and iridium(iii) complexes: siliconversusgermanium and simple κ1-coordinationversuscyclometallation

“…Reactions of two equivalents of germylene 1Ge, which was prepared from Ge( t Bu2bzam)Cl 18 and LiMes, 19 1 Ge-Ge( t Bu2bzam) t Bu}], only differing from 2Ge and 3Ge, respectively, in the substituent attached to the Ge( t Bu2bzam) fragment ( t Bu instead of Mes), have been previously reported by our group. 20 These results clearly contrast with those obtained when silylene 1Si was treated with the same metal precursors under identical experimental conditions, since these reactions led, with no observation of k 1 Si-silylene intermediates, to the cyclometallated products…”

“…The plane defined by the Mes group ring, is not bisecting the NGeN angle (C21−C16− Ge1−C5 torsion angle of 152.5(3)°), in contrast with what is observed in the free ligand 1Ge, which has Cs symmetry. 19 The Ir −Ge bond distance, 2.4255(5) Å, is slightly beyond the range of Ir−Ge distances (2.331(3)−2.4203(3) Å) found for the six iridium complexes equipped with terminal germylenes that have hitherto been crystallographically characterized. 14,16,20,21 The 1 H NMR spectrum of 2Ge in CD2Cl2 at room temperature shows three broad peaks for the the four cod ligand olefinic protons ( Please do not adjust margins Please do not adjust margins (although they may vibrate) and that the Mes group does not rotate about the Ge-Cipso bond.…”

“…All reaction products were vacuumdried for several hours prior to being weighed and analysed. The metal complexes [Ir2(µ-Cl)2(h 4 -cod)2], 24 [Ir2Cl2(µ-Cl)2(h 5 -Cp*)2], 25 [Ir2(µ-Cl)2(h 2 -coe)4], 25 4Si 15 and 5Si, 15 LiMes 26 and the germylenes Ge( t Bu2bzam)Cl 18 and 1Ge 19 were prepared following published procedures. All remaining reagents were purchased from commercial suppliers.…”

Cyclometallation of Heavier Tetrylenes: Reported Complexes and Applications in Catalysis

“…Complex 14 is a remarkable iridium (V) complex featuring a distorted pentagonal bipyramidal ligand environment with two k 2 C,Si-silylenes and a hydride at the equatorial positions and a chloride and another hydride at axial positions. Aiming at comparing C Si and C Ge in cyclometallation reactions, our group published in 2018 [38] a reactivity study involving the isostructural germylene C Ge (prepared [40] in 65 % yield by transmetallation of LiMes with Ge(tBu 2 bzam)Cl [36] ). In contrast with the above results using C Si , the room temperature reactions of this germylene with [Ir 2 (μ-Cl) 2 (η 4 1).…”

Nitrile formation via dichlorocarbene insertion into the Si–N bond of Ln(iii) bis(trimethylsilyl)amide complexes

“…7 e ,12 Silylenes Si( t Bu 2 bzam)R 1 (R 1 = Mes, CH 2 SiMe 3 ) could also attack the C carbene atom of the Fischer alkynyl (ethoxy) carbene complex [M(CO) 5 {C(OE t )C 2 R 2 }] (M = W, Cr; R 2 = Ph or ferrocenyl, Fc) to give the Si–N bond insertion products with striking rearrangement. 13 Regarding the formation of nitriles, there has been no relevant report on the carbene insertion reactions into the N–H bond, not to mention the rarely explored Si–N bond although some precedents on Si–N cleavage and transformation have been reported. 14…”