Synthesis and Reactivity of Monocarbollide Carbonyl Complexes of Iron and Molybdenum with Icosahedral Frameworks

Abstract

The [NEt4]+ (1a), [NHMe3]+ (1b), and [N(PPh3)2]+ (1c) salts of the monoanion [Fe(CO)3(η 5-7-CB10H11)]- have been prepared via the reaction between [Fe3(CO)12] and [NHMe3][nido-7-CB10H13] in THF (tetrahydrofuran). The complexes [N(PPh3)2][Fe(CO)2(L)(η 5-7-CB10H11)] (L = PPh3 (2), CNBut (3)) were obtained by treating 1c in THF with PPh3 and CNBut, respectively, in the presence of Me3NO. The compound [N(PPh3)2][Mo(CO)4(η 5-7-CB10H11)] (4) has been synthesized from [Na]3[nido-7-CB10H11] and [Mo(CO)3(NCMe)3] in the presence of CO and with addition of HBF4·Et2O and [N(PPh3)2]Cl. An X-ray diffraction study established that in the anion of 4 the Mo atom is coordinated on one side by the four CO molecules and on the other by a nido-7-CB10H11 carborane in a η5 manner. In reactions with PPh3 and CNBut, the salt 4 gives the species [N(PPh3)2][Mo(CO)3(L)(η 5-7-CB10H11)] (L = PPh3 (5a), CNBut (6)). Salts of the anions [Fe(CO)3(η 5-7-CB10H11)]- and [Mo(CO)3(PPh3)(η 5-7-CB10H11)]- react with donor molecules (THF, OEt2, SMe2) in the presence of acids and other hydride abstracting reagents to give zwitterionic complexes: [Fe(CO)3(η 5-9-L-7-CB10H10)] (L = O(CH2)4 (7), OEt2 (8), SMe2 (9)) and [Mo(CO)3(PPh3)(η 5-9-L-7-CB10H10)] (L = O(CH2)4 (10), OEt2 (11)), formed as single isomers. That the donor molecules L are bonded to a boron atom which lies in a β-site with respect to the carbon in the ring ligating the metal was established by X-ray diffraction studies on 7 and 10. In the latter the PPh3 molecule is transoid to the BO(CH2)4 group, presumably for steric reasons. Alkyne−molybdenum complexes [N(PPh3)2][Mo(CO)2(ButC⋮CH)(η 5-7-CB10H11)] (13) and [N(PPh3)2][Mo(CO)2(PhC⋮CR)(η 5-7-CB10H11)] (R = H (14), Ph (15)) have also been prepared.

Contemporary bimetallic molecules: an unusual class of exo-closo metallacarbaboranes having no metal–metal bonds

“…This is at variance with the behaviour of the complexes 6 and 7 towards hydride abstracting reagents, where a hydride is almost always removed from a β-B site in the CBBBB ring and replaced by a charge-compensating neutral donor molecule such as THF. 4 This may be because the binding of an exo-ML n fragment is more sterically controlled.…”

“…Treatment of its caesium salt Cs [3,3,3 We are concurrently developing the chemistry of monocarbon metallacarbaborane complexes, a class of compound that has been little studied up to the present time. Species prepared recently in our laboratory include [N(PPh 3 ) 2 ] 2 [2,2,2-(CO) 3 -closo-2,1-ReCB 10 H 11 ] 5, 3 4 These compounds contain closo-2,1-MCB 10 cage frameworks, as opposed to the more familiar closo-3,1,2-MC 2 B 9 systems, and it was of interest to determine whether they like 1 would react with appropriate reagents to give zwitterionic bimetal compounds. In this paper we report studies with 6 and 7.…”

Metal Complexes of Monocarbon Carboranes: A Neglected Area?

“…[5] Thus, treatment of the iron species with the hydride abstracting agents fMeCNMeg þ or fPPh 2 g þ (from MeCN=MeOSO 2 CF 3 or ClPPh 2 =TlPF 6 , respectively) affords neutral, boron substituted derivatives (Scheme 1) in which the cluster substituent can undergo further transformations (e.g., imine!amine) thereby introducing functionality at the cluster surface. [5,9,10] The dianionic rhenium cluster on the other hand has been shown to combine with transition-metal cations to give bi-and tri-metallic species such as those shown in Scheme 2. [5,11] Scheme 1.…”

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“…Reaction of these anionic salts with donor molecules (X) in the presence of hydride abstracting reagents affords the complexes [Fe(CO) 2 (PPh 3 )(h 5 -9-X-7-CB 10 H 10 )] 2 (X = THF, OEt 2 or SMe 2 ) and [Mo(CO) 3 (PPh 3 )(h 5 -9-X-7-CB 10 H 10 )] 2 (X = THF or OEt 2 ). 87 In a related paper, reaction of these two monoanionic metallacarboranes with copper phosphine, gold phosphine, ruthenium phosphine and {CpFe(CO) 2 } + fragments to afford neutral, zwitterionic, bimetallic complexes with exo substituents co-ordinated to the cage has been described. 88 The reaction of the anionic metallaborane Cs ] results.…”