Anionic amino acid [closo-1-CB 9H 8-1-COO-10-NH 3]- and dinitrogen acid [closo-1-CB 9H 8-1-COOH- 10-N 2] as key precursors to advanced materials: synthesis and reactivity

Bryan Ringstrand, Piotr Kaszynski, Victor G. Young, Zbynek Janoušek

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Abstract

Amino acid [closo-1-CB gH 8-1-COO-10-NH 3]- (4) was prepared by amination of iodo acid [closc-1-CB gH 8-1-COOH10-l]- (1) with LiHMDS in a practical and reproducible manner. The apparent dissociation constants, pK 2 = 5.6 and PK 1 > 11, were measured for 4[NMe 4] in 50% aq. EtOH. Diazotization of 4 with NO +PF 6- under mildly basic conditions afforded stable dinitrogen acid [closo-1-CB 9H 8-1-COOH-10-N 2] (5). Activation parameters (ΔH‡ = 33.9 ± 1.4 kcal mol -1 and ΔH‡ = 10 ± 3.5 cal mol -1 K -1) for thermolysis of its methyl ester [ctoso-1-CB 9H 8-I-COOMe-10-N 2] (11) in PhCN were established, and the heterolysis of the B-N bond is believed to be the rate-determining step. Electrochemical analysis showed a partially reversible reduction process for 11 (E 1/2 red = -1.03 V) and 5(E 1/21 red = -1.21 V), which are more cathodic than reduction of [closo-1-CB 9H 9-1-N 2] (17). The dinitrogen acid 5 was reacted with pyridine and N, N-dimethylthioformamide, to form pyridine acid 6 and protected mercapto acid 6, respectively, through a boronium ylide intermediate 18. Compound 7 was converted to sulfonium acid 8. The molecular and crystal structures for 5 [C 2H 9B 9N 2O 2 monoclinic, P2 1In, a = 7.022(2) ̊,D = 11.389(4) Å, c = 12.815(4) Å, β = 96.212(5)°; V = 1018.8(6) Å 3, Z= 4,], 6 [C 7H 14B 9NO 2, monoclinic, P2 1In, a = 14.275(4) ̊, b=12.184(3) Å, c = 30.538(8) Å, β = 95.377(4)°; V= 5288(3) ̊ 3, Z= 16], and 8 [C 7H 19B 9O 2S, monoclinic, P2 1/c a = 15.988(5) Å, b = 19.377(6) Å, c=9.655(3) A, β = 98.348(5)°; V= 2959.4(16) Å 3, Z= 8] were determined by X-ray crystallography and compared with results of density functional theory (DFT) and MP2 calculations. Electronic structures of 5, 6, and related species were elucidated with electronic spectroscopy and assessed computationally at the B3LYP/6-31 G(d, p), MP2/6-31G(d,p), and ZINDO//MP2 levels of theory.

Original languageEnglish (US)
Pages (from-to)1166-1179
Number of pages14
JournalInorganic chemistry
Volume49
Issue number3
DOIs
StatePublished - Feb 1 2010

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