Synthesis of Overloaded Cyclopentadienyl Rhodium(III) Complexes via Cyclotetramerization of tert-Butylacetylene

Abstract

Herein we describe the synthesis and reactivity of rhodium catalysts with the very bulky cyclopentadienyl ligand C 8 H 3 t Bu 4 (designated as t Bu 4 Cp). The reaction of [Rh(cod)Cl] 2 with tert-butylacetylene in the presence of Et 3 N gives the complex ( t Bu 4 Cp)Rh(cod) (60−65% yield), in which the cyclopentadienyl ligand t Bu 4 Cp is assembled from four alkyne molecules. The oxidation of ( t Bu 4 Cp)Rh(cod) with chlorine or bromine gives the corresponding halide complexes ( t Bu 4 Cp)RhX 2 (X = Cl (85%), Br (95%)), which have unusual 16-electron monomeric structures due to the steric shielding provided by t Bu groups. A similar reaction with iodine gives the ionic dinuclear complex [( t Bu 4 Cp)RhI 3 Rh-( t Bu 4 Cp)]I (99%) with halide bridges. The bromide complex ( t Bu 4 Cp)RhBr 2 reacts with phosphorus ligands such as P(OMe) 3 , P(OPh) 3 , PMe 2 Ph, and PMePh 2 to give the 18-electron adducts ( t Bu 4 Cp)RhBr 2 (PR 3 ), but no reaction occurs with larger phosphines such as PPh 3 . The racemic chloride ( t Bu 4 Cp)RhCl 2 can be separated into enantiomers by preparative TLC of its diastereomeric adducts with (R)-phenylglycinol. The complex ( t Bu 4 Cp)RhBr 2 catalyzes C−H activation and annulation of Opivaloyl-hydroxamate as well as insertion of phenyldiazoacetate into E−H bonds, although the reaction rates and the substrate scope are limited by the bulky t Bu 4 Cp ligand.

Synthesis of the Sterically Shielded Rhodium(I) Arene Complex by Cycloaddition of the Phosphorous‐Substituted Alkyne

“… [5,6] Unfortunately, these results were published only as the short communication with little experimental details and no crystal structures. Recently, we and others have synthesized a variety of catalytically active rhodium complexes by cyclization of alkynes into cyclobutadiene and cyclopentadienyl ligands in the coordination sphere of the metal [7–11] . Therefore, we became interested in the detailed reinvestigation of the results reported by Dr. Winter.…”

“…Recently, we and others have synthesized a variety of catalytically active rhodium complexes by cyclization of alkynes into cyclobutadiene and cyclopentadienyl ligands in the coordination sphere of the metal. [7][8][9][10][11] Therefore, we became interested in the detailed reinvestigation of the results reported by Dr. Winter.The starting ortho-diphenylphisphino-tolane (1) was obtained by the literature procedure from 2-bromo-iodobenzene in two steps. [12] Further reaction of 1 with Rh(PPh 3 ) 3 Cl proceeded at room temperature and gave the metallacycle 2, which was isolated in 92 % yield as air-stable orange crystals.Unfortunately, the analogous reaction of 1 with Co(PPh 3 ) 3 Cl led to a complex mixture of products according to 31 P NMR.…”

“…Recently, we and others have synthesized a variety of catalytically active rhodium complexes by cyclization of alkynes into cyclobutadiene and cyclopentadienyl ligands in the coordination sphere of the metal. [7][8][9][10][11] Therefore, we became interested in the detailed reinvestigation of the results reported by Dr. Winter.…”

Catalytic and Stoichiometric Reactions of the Parent Olefin Rhodium(I) Complex with Alkynes

“…1 H NMR ((CD 3 ) 2 CO, 400 MHz): δ = 6.44 (s, 10H, Cp), 6.29 (s, 5H, Cp), 3.18 (q, 4H, J = 7.7 Hz, CH 2 ), 2.52 (q, 4H, J = 7.6 Hz, CH 2 ), 1.49 (t, 6H, J = 7.6 Hz, CH 3 ), 0.95 (t, 6H, J = 7.5 Hz, CH 3 ) ppm. 13 C NMR ((CD…”

A Class of Readily Tunable Planar‐Chiral Cyclopentadienyl Rhodium(III) Catalysts for Asymmetric C–H Activation

“…However, in sharp contrast to the great success achieved in the type I catalyst, the type II catalyst is largely underdeveloped due to its high challenges. The only examples are catalysts J [12] and K [13] reported by Perekalin (Figure 1c), which were optically resolved respectively by recrystallization of its diastereomeric adducts with ( S )‐proline, and by preparative thin layer chromatography (TLC) of its diastereomeric adducts with ( R )‐phenylglycinol. The catalyst J was found to be highly efficient for the asymmetric reaction of aryl hydroxamic acid with strained alkene.…”