Amine–nitrile coupling in amino-monocarbollide complexes of molybdenum

Abstract

The Mo 0 molybdenacarbaborane trianion [1-NH 2 -2,2,2-(CO) 3 -closo-2,1-MoCB 10 H 10 ] 3Ϫ is formed in situ from the reaction between [7-NH 2 -nido-7-CB 10 H 10 ] 3Ϫ and [Mo(CO) 4 {NH(CH 2 ) 5 } 2 ] in THF solution (THF = tetrahydrofuran). In the absence of nitriles, oxidation of this trianion by CH 2 ᎐ ᎐ CHCH 2 Br gives the Mo II complex [1,2-µ-NH 2 -2,2,2-(CO) 3 -closo-2,1-MoCB 10 H 10 ] Ϫ , isolated as its [N(PPh 3 ) 2 ] ϩ salt. However, in the presence of nitriles NCR, the same oxidation ultimately affords the species [N(PPh 3 ) 2 ][1,2-µ-{NHC(R)᎐ ᎐ NH}-2,2,2-(CO) 3 -closo-2,1-MoCB 10 H 10 ] in which amidine groups form a bridge between the carbon atom of the cage and the molybdenum, as a consequence of coupling of the nitrile with the cage-bound NH 2 group. The acetamidine product [N(PPh 3 ) 2 ][1,2-µ-{NHC(Me)᎐ ᎐ NH}-2,2,2-(CO) 3 -closo-2,1-MoCB 10 H 10 ] is also formed by reaction of [7-NH 2 -nido-7-CB 10 H 12 ] Ϫ with [Mo(CO) 6 ] in refluxing NCMe, and its structure was confirmed by an X-ray diffraction study. Further oxidation of this species by I 2 in the presence of CNBu t gives the Mo IV derivatives [1,2-µ-{NHC(Me)᎐ ᎐ NH}-2,2-(CNBu t ) 2 -2-L-2-I-closo-2,1-MoCB 10 H 10 ] (L = CO, CNBu t ), of which the tris(isocyanide) complex has been studied by X-ray diffraction.

Actinide‐Mediated Cyclization of 1,2,4,5‐Tetracyanobenzene: Synthesis and Characterization of Self‐Assembled Trinuclear Thorium and Uranium Macrocycles

“…12 The formation of an actinide ketimide complex ( 5 ) seems to be the crucial step in the synthesis of the unique 5,6‐dicyano‐1‐methyl‐3‐( N ‐methylamino)isoindolyl ligand. Numerous examples of metal‐mediated nitrile coupling reactions with compounds such as amines,13a imines,13b ketones,13c alkynes,13d amidines,13e oximes,13f and other nitriles13g are known. However, to the best of our knowledge, the coupling of a nitrile with a ketimide functional group has not been observed with transition metals, once again highlighting the differences between transition metals and the actinides.…”

Alkyne coupling at a rhenium–monocarborane substrate: synthesis of Re,B-η2:σ-butadienyl complexes

“…2a One exciting feature of the latter system is the potential for the pendant -NR 2 group to form an additional intramolecular bond with the metal centre, so that overall the carborane ligand can function formally as an eight-electron (6p + 2r) donor. [4][5][6] This may permit the stabilization of early transition-metal centres and metals in relatively high oxidation states. Herein we report a set of Re III -monocarbollide species in which a carboranebound NHBu t unit forms an intramolecular bridge between the cage carbon atom and the rhenium vertex.…”

Metal complexes of monocarbon carboranes bearing C-amine or -amino substituents

“…In the anion the two {1,2-lNHBu t -2,2,2-(CO) 3 -closo-2,1-MoCB 10 H 10 } units are coordinated to the central Au atom in an approximately linear manner [Mo-Au-Mo = 170.80(2)°]. The structure of the anion is related to those of the isolobal cyclopentadienide anionic complexes [l-Au-{M(CO) 3 -(g 5 -C 5 H 5 )} 2 ] À (M = Cr, Mo, W)[33].Similar methods to those that afforded 15a but employing the carbaborane anions [7-NH 2 -nido-7-CB 10 H 10 ] 3À or [7-NH 2 -nido-7-CB 10 H 12 ] À , respectively, failed to yield [10 H 10 ] (24a)[34]. This and the related species 24b,c arise from a coupling of the cage-carbon bound NH 2 group with a nitrile molecule NCR.…”

“…Thus, the room temperature reaction of Li 2 [7-NMe 3 -nido-7-CB 10 H 10 ] with [Mo(CO) 4 {NH(CH 2 ) 5 } 2 ] in thf, followed by oxidation with CF 3 SO 3 Me or CH 2 ‚CH CH 2 Br, gave the anion [2,3-l-{N(CH 2 ) 5 }-2,2,2-(CO) 3 -closo-2,1-MoCB 10 H 10 ] À , which can be isolated as its [N(PPh 3 ) 2 ] + salt (34). The same anion may be obtained from the direct reaction of 7-NMe 3 -nido-7-CB 10 H 12 with [Mo(CO) 4 {NH(CH 2 ) 5 } 2 ] in refluxing thf.…”

“…It was of interest to determine how 24a would behave with the same reagents [34]. Two neutral Mo IV products were obtained: [1,2-l-{NHC(Me)‚NH}-2,2-(CNBu t ) 2 -2-L-2-I-closo-2,1-MoCB 10 H 10 ] (25a, L = CO: 25b, L=CNBu t ).…”