Metal atom synthesis of metallaboron clusters. 6. Synthesis and structural characterization of a coupled diborane-metallacarborane cluster: 5:1',2'-[1-(.eta.-C5H5)Co-2,3-(Me3Si)2C2B4H3][B2H5]

Abstract

The reaction of thermally generated cobalt atoms with hexaborane(lO), bis(trimethyhilyl)acetylene, and cyclopentadiene has been found to give as major products the cobaltacarborane clusters 5:1',2'-[ 147-C5H5)Co-2,3-(Me3Si)zCzB4H3][B2H5], I, 1-(q-C5H5)Co-4,6-(Me3Si)2c2B6H6, 11, and l-(tpC5H5)Co-4,5-(Me3Si)2C2B6H6, 111, along with smaller amounts of 5-(q-C5H5)C~-l,8-(Me3Si)2C2B5H5, IV, and 1-(q-C5H5)Co-2,3-(Me3Si)2C2B4H4, V. The spectroscopic data for compounds 11,111, IV, and V are consistent with their formulations as closo polyhedral cage systems in which one bis(trimethylsily1)acetylenic unit has been inserted into the cage framework. A single-crystal X-ray study of I has revealed, however, that it has a unique bridged structure composed of a ~loso-l-(q-C~H~)Co-2,3-(Me~Si)~C~B~H~-sandwich complex which has an exopolyhedral -B2H5 group bound to the 5-boron cage atom by means of a boron-boron-boron three-center bond. Compound I can thus be considered a bridge-substituted organometallic derivative of diborane. Crystal data for I: s ace group C2/c; 2 = 8; a = 29.890 (9) A, b = 9.213 (2) A, c = 15.127 (6) A, / 3 = 91.57 (3)O; V = 4164.4 13. The structure was refined by full-matrix least-squares techniques to a final R of 0.033 and R, of 0.042 for the 4005 unique reflections which had F,2 > 30(F$). IntroductionWe have previously reported that the reaction of metal atoms with boron hydrides, acetylenes, and either cyclopentadiene or arenes can lead to the incorporation of a n acetylenic unit into the metallaboron cluster framework to yield (+25H5)metallacarborane2 or ($-C6R6)metallacarborane c~m p l e x e s .~ In general, the yields of metalcontaining products in these reactions were found to be low owing, in part, to competing metal atom promoted alkyne oligomerizations. For example, in reactions employing 2 -b~t y n e ,~*~ hexamethylbenzene was found to be the major product. This observation prompted our investigation of the reactions of metal atoms and boron hydrides with alkynes, such as bis(trimethylsilyl)acetylene, which would be more resistant to cyclization, with the aim

Synthesis of Novel Molybdaboranes from (η5-C5R5)MoClnPrecursors (R = H, Me;n= 1, 2, 4)

“…In common with most other structurally characterized B 2 H 5 units, the H 2 B···BH 2 unit is planar and approximately perpendicular to the plane defined by the unit. The B···B distance within the B 2 H 5 unit [1.79(3) Å] is consistent with those obtained for other related compounds. − Furthermore, the B(2)−B(3) and B(2)−B(4) distances [1.77(2) and 1.87(2) Å, respectively] are similar to the analogous values in [CpCo(Me 3 Si) 2 C 2 B 4 H 3 ][B 2 H 5 ] [1.789(2) and 1.799(2) Å 35 ] and also to those in B 3 H 7 CO [1.820(6) and 1.803(6) Å 36 ]. In common with these compounds the B 2 H 5 unit in 4 is viewed as being linked to the third boron atom via a three-center boron−boron−boron bond.…”

“…The B‚‚‚B distance within the B 2 H 5 unit [1.79( 3) Å] is consistent with those obtained for other related compounds. [34][35][36] The single-crystal X-ray diffraction structure of 3 is reproduced in Figure 2; relevant interatomic distances and angles are listed in Table 6. The asymmetric unit contains two independent (Cp*MoCl) 2 B 2 H 6 molecules which differ little in terms of geometric parameters (Table 6 lists *TaBr) 2 B 2 H 6 32 and (C 5 Me 4 -EtNbCl) 2 B 2 H 6 (Cp*MoCl) 2 B 3 H 7 (5).…”

Directed Synthesis of Chromium and Molybdenum Metallaborane Clusters. Preparation and Characterization of (Cp*Cr)2B5H9, (Cp*Mo)2B5H9, and (Cp*MoCl)2B4H10

“…The H 2 B···BH 2 unit is planar and approximately perpendicular to the plane defined by the BBHB unit. Furthermore, the B(2)−B(3) and B(2)−B(4) distances are similar to the analogous values in both [CpCo(Me 3 Si) 2 C 2 B 4 H 3 ][B 2 H 5 ] and B 3 H 7 NH 3 in which the B 2 H 5 unit is viewed as being linked to a third boron atom via a three-center boron−boron−boron bond. It seems likely that a similar bonding situation occurs in 4 .…”

Expansion of iridaborane clusters by addition of monoborane. Novel metallaboranes and mechanistic detail

“…Metallaborane chemistry is an interesting and diverse area of cluster chemistry which is closely allied to both polyhedral metal compounds as well as boron hydrides. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Developments in this chemistry continue to demonstrate that close electronic and structural relationships exist between organometallic compounds and those formed from metal and polyhedral borane fragments despite the fact that "electron deficient" boranes are not considered ligands in the normal sense of coordination chemistry. 18 Thus, unlike their organometallic siblings, they are almost always better considered as clusters.…”