Abstract
The metalation of [Tl]2[1-(1′-3′,1′,2′-closo-TlC2B9H10)-3,1,2-closo-TlC2B9H10], with the smaller {Ni(dmpe)} fragment sourced from [Ni(dmpe)Cl2], is explored. The bis(metalated) products are obtained as a diastereoisomeric mixture. These isomers were separated, fully characterised spectroscopically and crystallographically and identified as rac-[1-(1′-3′-(dmpe)-3′,1′,2′-closo-NiC2B9H10)-3-(dmpe)-3,1,2-closo-NiC2B9H10] (1) and meso-[1-(1′-3′-(dmpe)-3′,1′,2′-closo-NiC2B9H10)-3-(dmpe)-3,1,2-closo-NiC2B9H10] (2). Previously, these 3,1,2-NiC2B9-3′,1′,2′-NiC2B9 architectures (where both cages are not isomerised), were inaccessible, and thus new structures can be achieved during bis(nickelation) with {Ni(dmpe)}. Further, the metalation of the tetra-thallium salt with the bulky {Ni(dppe)} fragment sourced from [Ni(dppe)Cl2] was also studied. These bis(nickelated) products were also fully characterised and are afforded as the stereospecific species rac-[1-(1′-3′-(dppe)-3′,1′,2′-closo-NiC2B9H10)-3-(dppe)-3,1,2-closo-NiC2B9H10] (3) and [1-(2′-4′-(dppe)-4′,1′,2′-closo-NiC2B9H10)-3-(dppe)-3,1,2-closo-NiC2B9H10] (4α). In the latter metalation, compound 3 shows intramolecular dihydrogen bonding, contributing to the stereospecificity, whereas isomerisation from 3,1,2 to 4,1,2- in the 4α is related to steric relief.
Highlights
Since the discovery of bis(carboranes) in 1964, the chemistry of 1,10 -bis(o-carborane)(Scheme 1, a) has evolved rapidly, once a high-yielding synthetic route was devised in 2003
The bimetallic metallacarboranes derived from the metalation of doubly deboronated 1,10 -bis(o-carborane) with both rhodium and ruthenium fragments are 3,1,2-MC2 B9 -20,10,80 -MC2 B9 [M = {Rh}, {Ru}] species, in which one of the cages has isomerised (Scheme 1, b and c)
Later, [Tl]+ salts were chosen for metalation because of their generally better yields [9]
Summary
Since the discovery of bis(carboranes) in 1964, the chemistry of 1,10 -bis(o-carborane). Since 2010, the Welch group have established many variations of the metalation chemistry of 1,10 -bis(o-carborane), one approach being cage expansion chemistry via reductionmetalation of this species [1], whilst another metalation strategy explored broadly within the group is deboronation/metalation of 1,10 -bis(o-carborane). The single deboronation/metalation of 1,10 -bis(o-carborane) has been reported for cobalt, nickel and ruthenium metal fragments and afforded a wide range of mono-metallicbis(carborane) isomers [7,8]. Double deboronation/metalation was achieved, such that both cages became metallacarboranes. The bimetallic metallacarboranes derived from the metalation of doubly deboronated 1,10 -bis(o-carborane) with both rhodium and ruthenium fragments are 3,1,2-MC2 B9 -20 ,10 ,80 -MC2 B9 [M = {Rh}, {Ru}] species, in which one of the cages has isomerised (Scheme 1, b and c). An example of stepwise deboronation/metalation-deboronation/heterometalation is reported [11].
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