Synthese, Reaktivität und Komplexeigenschaften von nido‐2,3,5‐Tricarbahexaboranen

Abstract

Syntheses, Reactivity a n d Complexation Properties of nido-2,3.5-Tricarbahexaboranes* By double hydroboration of 1,3-dihydro-1,3-diborafulvenes 2 or 4,5-diisopropylidene-1,3-diborolanes 3 with (Et2BH)2 and subsequent loss of triethylborane derivatives 1 of 2,3,5-tricarbahexaborane are formed under mild conditions. The stability of the nido-carboranes 1 depends on the substituents in the basal positions. After deprotonation, the tricarbahexaboranate ion (1 -H)functions as a cyclopentadienyl analogue (C,H,)-, and its reaction with allylnickel bromide dimer gives the allylnickel complexes 8a, b. Reaction of octacarbonyl dicobalt with 1 b yields the dicarbonylcobalt complex lob. Treatment of l e with [(C,H,)Ni(CO)]2 results in the formation of the dinuclear carbonyl-bridged complex 12 e. Von den Vertretern der nido-Carborane rnit pentagonaler Basisflache sind vor allem Derivate des C2B9Hl3['I und des C2B4H8r21 zum Aufbau von closo-Metallacarboranen untersucht ord den[^-^]. In der Reihe der nido-Cluster C,B6 nHlo fehlten bislang Derivate von 2,3,5-Tricarbahexaboran (n = 3), wahrend Beispiele fur das 2,3,4-Isomer schon seit 1968 bekannt sind@'. Wir haben 1984 erstmals die Bildung von (2,3,5-Tricarbahexaboranyl)nickel-Komplexen aus der Bis(2,3-dihydro-1,3-diborol)nickel-Verbindung A be~bachtet~". Dabei entsteht durch Eliminierung von Wasserstoff aus A und Uberdachung des postulierten Bis(2,3-dihydro-1,3-di-boroly1)nickeLSandwichs (1 6 VE) rnit einer Methylborandiyl-Einheit [Me-B] der 18-VE-Komplex B. Des weiteren bilden sich durch Stapelreaktionen die Oligodecker-Komplexe C (n = 1 -8). In

Small boranes, carboranes, and heterocarboranes

“…As in 11, the ratio of boron to carbon vertices is 1:1 in the nido-2,3,5-tricarbahexaboranes(7) 12 [23]. Any carborane with three carbon vertices requires the presence of an extra hydrogen atom, which is located on the pentagonal face and bonded to the C5 carbon atom.…”

“…Deprotonation of 12 leads to the tricarbahexaboranyl anion (12-H) -. As it is isolobal with the C 5 H 5 -a number of closo-metallacarboranes have been prepared [23]. Several syntheses have been explored for nido-tricarbahexaboranes, one occurs by hydroboration of 3,4-bis(isopropylidene)-1,3-diborolanes to give 12 [23].…”

“…The synthesis and reactivity of (EtC) 4 (BCl) 4 (11a) is reported. The chemistry of nido-tricarbahexaboranes 12 has been developed [23], and we describe some aspects of the chemistry of the heterocarboranes 13 (X = NMe) and 14 (X = S).…”

1,3-Diboraheterocycles as ligands in metal complexes involving endo-C–H bonds

“…In solution at ambient temperature the complexes slowly lose hydrogen and the resulting 16 VE sandwich is capped by a boranediyl from another molecule to yield an 18 VE carboranyl complex as shown in Scheme 1. A second capping leads to a di(2,3,5-tricarba-hexaboranyl)nickel complex [12] (Fig. 2).…”

“…1) start with 1,4-diborafulvenes and 4,5-bis(isopropylidene)-1,3-diborolanes, which are doubly hydroborated with (HBEt 2 ) 2 . Elimination of BEt 3 yield oily tricarba-nido-hexaboranes [12], showing a high-field multiplet near -1.35 ppm. This 1 H NMR shift is indicative of an endo-hydrogen, which according to calculation is in a C-H-B bridging position [9].…”