Novel Mono-alkyl Magnesium Complexes Stabilized by a Bulky β-Diketiminate Ligand:  Structural Characterization of a Coordinatively Unsaturated Trigonal System

Abstract

Despite the synthetic importance and widespread use of Grignard reagents, and the fact that magnesium alkyls have been known since the middle of the 19th century, 1 the chemistry of well characterized simple mono-alkyl magnesium systems is surprisingly undeveloped. 2 Indeed, it appears that only a handful of halide-free, uncharged mono-nuclear systems are known, these being based on pyrazolylborate, 3 carbazolyl 4 or triazinyl 5 ligands. 6 None of these systems is formally coordinatively unsaturated. Furthermore, alkyl-bridged dimeric systems are virtually unknown for simple mono-alkyl magnesium. 7,8 Our studies have been directed toward the formation of coordinatively unsaturated, and also alkyl bridged or solvent coordinated mono-alkyl magnesium complexes (i.e. systems that have a vacant coordination site or effectively a protected vacant site), these being designed as potential catalytic agents. In such systems a suitable ancilliary ligand could both stabilize the desired molecular arrangement and also influence the activity and selectivity of the reagent. A bulky β-diketiminate ligand 9 has been used to this effect in the present work. Here we report the first examples, for halide-free monoalkyl magnesium systems, of: (i) a coordinatiVely unsaturated mononuclear complex and (ii) an alkyl-bridged dimer, 7 as well as a solvent coordinated derivative.

Group 1 and 13 complexes of aryl-substituted bis(phosphinimino)methyls

“…1 is a monomeric lithium derivative of II in which the lithium centre is three-coordinate. This comprises a sixmembered metallocyclic structure in which the bis (phosphinimino)methyl ligand behaves as a strictly bidentate chelate and the lithium coordination is completed 110.69 (17) 102.5(2) m N(1)-P(1)-C(1) 114.3 (2) 112.90 (12) 106.90 (15) 107.84(15) n N(2)-P(2)-C(1) 119.0(2) 111.51 (12) 106.12(14) P(1)-C(1)-P (2) 115.8 (2) 134.58 (16) 130.74 (19) 118.71 (19) by a single molecule of diethyl ether. Although the chelated ligand adopts a boat conformation, the distance between the carbanionic methine carbon C(1) and the lithium centre is too long (2.999 A to suggest any significant interaction.…”

“…A review of the recent literature revealed a widespread use of chelating, anionic ligands derived by deprotonation of bulky aryl-substituted b-aminoimines such as I and related ligands bearing other flanking Nsubstituents, which have the potential for precise steric and electronic ÔtuningÕ of a reactive metal site. Ligands of this type have been used to support a variety of lowcoordinate transition metal [3][4][5][6][7][8][9][10][11][12][13], main group element [14][15][16][17][18][19][20] and f-element complexes [21,22]. Furthermore, many of these systems have shown great utility in, for example, ring opening polymerisation catalysis [23][24][25][26] or as synthetic mimics for low-coordinate metal environments encountered in biological systems [27][28][29][30].…”

Synthesis and Structures of Vinamidine MnII, ZnII, and CdII Iodine Derivatives

“…Recently we synthesized a monomeric Al I compound using 1 as a stable carbene analogue, and Gibson et al have prepared a mono-alkylmagnesium complex stabilized by 1. [5,6] Our research focused on the synthesis of complexes with low coordinate Mn, Zn and Cd atoms.…”

Synthesis and structural characterization of LiI, ZnII, CdII, and HgII complexes containing a fluorinated β-diketiminate ligand

“…Although the β-diketonato (B) [2] and β-enaminoketonato (C) [3][4] ligands are the traditionally popular chelating systems, the isoelectronic β-diketiminato ligands have recently gained dramatically increasing attention, due to the ease variation of R groups on the nitrogen, which may be hydrogen, alkyl, aryl, or silyl groups [5][6] . In the past decade, the use of β-diketiminates as supporting ligands was extensively studied, and a wide range of main group element [7][8][9][10][11] , transition metal [12][13][14][15][16] and lanthanide complexes [17][18] containing this type of ligands have been reported. Importantly, a good number of these metal complexes have proven to serve as effective catalysts for olefin polymerization [19] , silane dehydropolymerization [20] , olefin hydrosilylation [21] , lactide polymerization [22] , Suzuki coupling [23] , hydroamination [24] , and other transformations.…”