PARTIAL INSERTION OF THE 9-BBN UNIT INTO THE NIDO-B-10 FRAMEWORK - PREPARATION AND STRUCTURAL CHARACTERIZATION OF (9-BBN)B10H13 AND [(9-BBN)B10H12](-)

Na[B10H13] reacts with 9-Br-BBN (9-BBN = 9-bora[3.3. 1]bicyclononane) in CH2Cl2 to produce (9-BBN)B10H13, 1, in high yield. Single-crystal X -ray diffraction analysis shows that the baron atom of the 9-BBN unit in 1 is partially inserted into the nido-B-10 structure through a high ly asymmetric bridge between B(5) and B(6) on the B-10 cluster with di stances of B(BBN)-B(5) = 1.740(6) Angstrom and B(BBN)-B(6) = 2.079(6) Angstrom. There is also an agostic interaction of the terminal H(5b) o n B(5) with B(BBN). NMR studies confirm that this interaction is maint ained in solution. Compound 1 is unstable in coordinating solvents, re sulting in some cases in the cleavage of the 9-BBN unit from the decab orane skeleton. When 1 is placed in Et2O, NMR spectra suggest that (Et 2O)-(9-BBN)B10H13, 2, is formed in which an Et2O molecule associates w ith the baron B(BBN) of the 9-BBN unit while the interactions of that boron with B(6) and with H(5b) are eliminated, leaving only a direct b ond between B(BBN) and B(5). Reaction of 1 with ''Proton Sponge'', 1,8 -bis(dimethylamino)naphthalene, in CH2Cl2 gives [PSH][(9-BBN)B10H12], 3, (PSH = protonated ''Proton Sponge''). Single-crystal X-ray diffract ion analysis of 3 indicates a structure similar to that of nido-[B11H1 4](-), With the baron of the 9-BBN unit approximately occupying a vert ex site of the pentagonal face of a nido-B-11 cluster. The B(BBN) baro n is inserted into a bridging site between B(5) and its crystallograph ically imposed mirror equivalent B(10') of the decaborane cluster with B(BBN)B(5)/B(BBN)-B(10') distances of 1.884(4) Angstrom and a B(5)-B( 10') distance of 1.823(5) Angstrom. On the other hand the distance of the B(BBN) baron to B(6) and to the mirror equivalent B(9') is an abno rmally long 2.142(4) Angstrom, which indicates that the B(BBN) boron i s not fully accommodated in the formation of a nido-[B11H14](-) analog ue. The novel interaction of the 9-BBN fragment with the decaborane cl uster in 1 and the partial insertion of the 9-BBN moiety into the nido -B-10 unit observed in 3 are the first examples of sued interactions o bserved between a monoboron unit and a decaborane cluster. Crystal dat a: 1, Pbca (No. 61), a 11.924(3) Angstrom, b = 13.205(6) Angstrom, Na[ B10H13] reacts with 9-Br-BBN (9-BBN = 9-bora[3.3. 1]bicyclononane) in CH2Cl2 to produce (9-BBN)B10H13, 1, in high yield. Single-crystal X-ra y diffraction analysis shows that the baron atom of the 9-BBN unit in 1 is partially inserted into the nido-B-10 structure through a highly asymmetric bridge between B(5) and B(6) on the B-10 cluster with dista nces of B(BBN)-B(5) = 1.740(6) A and B(BBN)-B(6) = 2.079(6) Angstrom. There is also an agostic interaction of the terminal H(5b) on B(5) wit h B(BBN). NMR studies confirm that this interaction is maintained in s olution. Compound 1 is unstable in coordinating solvents, resulting in some cases in the cleavage of the 9-BBN unit from the decaborane skel eton. When 1 is placed in Et2O, NMR spectra suggest that (Et2O)-(9-BBN )B10H13, 2, is formed in which an Et2O molecule associates with the ba ron B(BBN) of the 9-BBN unit while the interactions of that boron with B(6) and with H(5b) are eliminated, leaving only a direct bond betwee n B(BBN) and B(5). Reaction of 1 with ''Proton Sponge'', 1,8-bis(dimet hylamino)naphthalene, in CH2Cl2 gives [PSH][(9-BBN)B10H12], 3, (PSH = protonated ''Proton Sponge''). Single-crystal X-ray diffraction analys is of 3 indicates a structure similar to that of nido-[B11H14](-), Wit h the baron of the 9-BBN unit approximately occupying a vertex site of the pentagonal face of a nido-B-11 cluster. The B(BBN) baron is inser ted into a bridging site between B(5) and its crystallographically imp osed mirror equivalent B(10') of the decaborane cluster with B(BBN)B(5 )/B(BBN)-B(10') distances of 1.884(4) Angstrom and a B(5)-B(10') dista nce of 1.823(5) A. On the other hand the distance of the B(BBN) baron to B(6) and to the mirror equivalent B(9') is an abnormally long 2.142 (4) A, which indicates that the B(BBN) boron is not fully accommodated in the formation of a nido-[B11H14](-) analogue. The novel interactio n of the 9-BBN fragment with the decaborane cluster in 1 and the parti al insertion of the 9-BBN moiety into the nido-B-10 unit observed in 3 are the first examples of sued interactions observed between a monobo ron unit and a decaborane cluster. Crystal data: 1, Pbca (No. 61), a 1 1.924(3) Angstrom, b = 13.205(6) Angstrom, c = 19.655(5) Angstrom, Z = 8; 3, Pnma (No. 62), a = 15.359(3) Angstrom, b = 13.932(3) Angstrom, c = 12.565(4) Angstrom, Z = 4.