Syntheses and Structures of Molybdenum Imido Alkylidene Pyrrolide and Indolide Complexes

Abstract

An X-ray structural study of Mo(NAd)(CHCMe2Ph)(2,5-Me2NC4H2)2 (1; Ad = 1-adamantyl) reveals it to contain one η1-2,5-Me2NC4H2 ring and one η5-2,5-Me2NC4H2 ring. The structures of Mo(NAr)(CHCMe2Ph)(pyrrolide)2 (Ar = 2,6-i-Pr2C6H3) complexes that contain 2,3,4,5-tetramethylpyrrolides, 2,5-diisopropylpyrrolides, or 2,5-diphenylpyrrolides are analogous to that of 1. In contrast, Mo(NAr)(CH2CMe2Ph)(indolide)2 (6) was shown to contain two η1-bound indolides. Monohexafluoro-t-butoxide pyrrolide (MAP) species can be prepared, either through addition of one equiv of Me(CF3)2COH to a bispyrrolide or through reactions between the lithium pyrrolide and the bishexafluoro-t-butoxide. A trimethylphosphine adduct of a bispyrrolide, Mo(NAd)(CHCMe2Ph)(η1-NC4H4)2(PMe3), has been prepared and structurally characterized, while a PMe3 adduct of MAP hexafluoro-t-butoxide species was found to have PMe3 bound approximately trans to the pyrrolide. This adduct serves as a model for the structure of the initial olefin adduct in olefin metathesis.

Molybdenum imido alkylidene and tungsten oxo alkylidene N-heterocyclic carbene complexes for olefin metathesis

“…While complexes 3a, 3b, 4, 5, 8, and 9 contain two triflate groups, compound 6 contains two different anionic ligands, i.e., one triflate and one hexafluro-2-propoxide group. As found for MAP-type catalysts [14,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], no ligand scrambling is observed. Cationic 7 is unique: it represents the first cationic Mo imido alkylidene catalyst that displays substantial olefin metathesis reactivity (vide infra).…”

High‐Oxidation State Molybdenum and Tungsten Complexes Relevant to Olefin Metathesis

“…Mo(NAr)(CHR ′ )(Pyr) 2 R ′ = t-Bu or CMe 2 Ph [11] Mo(N-2,6-Br 2 -4-MeC 6 H 2 )(CH-t-Bu)(Pyr) 2 [11] Mo(NAd)(CHCMe 2 Ph)(Pyr) 2 [11] Mo(NAd)(CHCMe 2 Ph)(Pyr) 2 (PMe 3 )* [12] Mo(NR)(CHCMe 2 Ph)(Pyr) 2 (bipy) R = Ar*, Ad, Ar Me2 , Ar Cl , Ar iPr , Ar tBu , Ar Mes [55] Mo(NAr)(CHCMe 2 Ph)X 2 X = Me 4 Pyr*, i-Pr 2 Pyr*, Ph 2 Pyr*, Indolide* [12] Mo(NAr)(CH-t-Bu)(Ph 2 Pyr) 2 [12] Mo(NAr)(CHCMe 2 Ph)(indolide) 2 (THF) [12] Mo(NAr)(CHCMe 2 Ph)(R 2 Pz) 2 R 2 Pz = 3,5-diphenylpyrazolide* or 3,5-di-t-butylpyrazolide [32] (continued overleaf ) [38] W(NC 6 F 5 )(CH-t-Bu)(Pyr) 2 (DME) [18] 1.2 New Imido Ligands and Synthetic Approaches 5 [34] (continued overleaf ) *An X-ray structure was obtained for this compound bipy, 2,2-bipyridyl; DME, 1,2-dimethoxyethane; Mes, 2,4,6-trimethylphenyl; NAd, N-1-Admantyl; NAr, N-2,6-i-Pr 2 C 6 H 3 ; NAr R2 , N-2,6-R 2 C 6 H 3 ; NAr R , N-2-RC 6 H 4 ; NAr 3,5Me2 , N-3,5-Me 2 C 6 H 3 ; Biphen 2− , 3,3 ′ -di-t-Bu-5,5 ′ ,6,6 ′ -tetramethyl-1,1 ′ -biphenyl-2,2 ′ -diolate; OBr 2 Bitet, 3,3 ′ -dibromo-2 ′ -(tert-butyldimethylsilyloxy)-5,5 ′ ,6,6 ′ ,7,7 ′ ,8,8 ′ -octahydro-1,1 ′ -binaphthyl-2-olate; OHIPT, hexaisopropylterphenoxide = O-2,6-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 2 ; OHMT, hexamethylterphenoxide = O-2,6-Mes 2 C 6 H 2 ; ODFT, decafluoroterphenoxide = O-2,6-(C 6 F 5 ) 2 C 6 H 3 ; ODPP, 2,6-diphenylphenoxide; ODIPP, O-2,6-(i-Pr) 2 C 6 H 3 ; OR F6 , OCMe(CF 3 ) 2 ; OR F3 , OCMe 2 (CF 3 ); OBiphenTMS, O-3,3 ′ -di-tert-butyl-5,5 ′ ,6,6 ′ -tetramethyl-2 ′ -(trimethylsilyloxy)biphenyl-2-olate; OBINAP-TBS, O-2 ′ -(tert-butyldimethylsilyloxy)-1,1 ′ -binaphthyl-2-olate; ODPP R , 2,6-(2,5-R 2 pyrrolyl) 2 Phenoxide (R = i-Pr or Ph); Pyr, pyrrolide; MesPyr, 2-mesitylpyrrolide; CNPyr, 2-cyanopyrrolide; Me 4 Pyr, 2,3,4,5-tetramethylpyrrolide; R 2 Pyr, 2,5-R 2 pyrrolide; TBS, dimethyl-t-butylsilyl; Trip, 2,4,6-triisopropylphenyl.…”

“…Other substituted pyrrolides form monomeric η 1 ,η 5 -bispyrrolides, except when the pyrrolides: (i) can only bind in an η 1 fashion, as is the case of the 2-mesitylpyrrolide (MesPyr) in Mo(NAr)(CHCMe 2 Ph)(η 1 -MesPyr) 2 [15], or (ii) are much more prone to bind in an η 1 fashion than an η 5 fashion, as in Mo(NAr)(CH 2 CMe 2 Ph)(η 1 -indolide) 2 [12]. If a donor functionality is present in the pyrrolide, then it can bind to another metal to form oligomers.…”

“…For example, Mo(NAd)(CHCMe 2 Ph)(2-CNPyr) 2 is an octamer in which two η 1 -pyrrolides are trans to one another at each metal center, and the cyano groups from neighboring Mo centers bind trans to the alkylidene and imido ligands [17]. Bis-η 1 -pyrrolides are also found as adducts, as in W(NAr)(CHCMe 2 Ph)(η 1 -MesPyr) 2 (dme) [37], Mo(NAd)(CHCMe 2 Ph)(η 1 -NC 4 H 4 ) 2 (PMe 3 ) [12], or one of the metals shown in Figure 1.1. The bispyrazolide complexes Mo(NAr)(CHCMe 2 Ph)(dppz) 2 and Mo(NAr)(CHCMe 2 Ph)(dtpz) 2 (dppz, 3,5-diphenylpyrazolide; dtpz, 3,5-di-t-butylpyrazolide) could be readily prepared from Mo(NAr)(CHCMe 2 Ph)(OTf ) 2 (dme) [8g].…”

“…The deprotonation of the alkylidene by the incoming pyrrolide nucleophile is especially problematic when one or two triflates is (are) present, and the pyrrolide is relatively sterically demanding [17]. Nevertheless, several bispyrrolides have been prepared in which the pyrrolides are relatively sterically demanding, for example, 2-mesityl [15][16][17], 2,5-diisopropyl [12], 2,5-diphenyl [12], or 2,3,4,5-tetramethyl [12]. The chemistry of complexes that contain one or two sterically demanding pyrrolides is underdeveloped with respect to the chemistry of the parent pyrrolide or 2,5-dimethylpyrrolide complexes, but the steric differences between various substituted pyrrolides could have significant consequences worthy of study.…”