Tetraarylpentaborates, [B(5)O(6)Ar(4)](-) (Ar = C(6)H(4)OMe-4, C(6)H(3)Me(2)-2,6): their formation from the reaction of arylboronic acids with an aryloxorhodium complex,structure, and chemical properties

The reactions of (4-methoxyphenyl)boronic acid (1a) and of (2,6-dimethylphenyl)boronic acid (1b) with (PMe(3))(3)Rh-(OC(6)H(4)Me-4) (2) in a 5:1 molar ratio result in the formation of cationic rhodium complexes with new tetraarylpentaborates [Rh(PMe(3))(4)](+)[B(5)O(6)Ar(4)](-) (3a, Ar = C(6)H(4)OMe-4; 3b, Ar = C(6)H(3)Me(2)-2,6). The characterization of 3a is as follows: orthorhombic space group P2(1)2(1)2(1), a = 14.7600(5) A, b = 17.1675(5) A, c = 19.8654(5) A; V = 5033.7(3) A(3); Z = 4. The characterization of 3b is as follows: orthorhombic space group Pnma, a = 23.704(6) A, b = 17.254(8) A, c = 13.304(2) A; V = 5441(2) A(3); Z = 4. An intermediate complex, [Rh(PMe(3))(4)](+)[Ph(3)B(3)O(3)(OC(6)H(4)Me-4)](-) (4), was isolated from the reaction of phenylboroxine, (PhBO)(3), with 2. The tetraarylpentaborates smoothly undergo hydrolysis to give [Rh(PMe(3))(4)](+)[B(5)O(6)(OH)(4)](-) (5).