Semi-sandwich platinum metals metallacarboranes derived from nido-C2B9H12−: Chemistry and structural studies

New Aspects of Ruthenium-Mediated Polyhedral Contraction of Monocarbollides

It has been shown that the interaction of tris(triphenylphosphine)ruthenium dichloride RuCl2(PPh3)3 (1) with 10-vertex monocarborane [6-Ph-nido-6-CB9H11]−[Et4N]+ (2) under mild thermolysis conditions is not selective due to the undesired coordination of ruthenium to a phenyl substituent in the carborane and phosphine ligands, giving the series of new classical and non-classical metallacarborane complexes. In contrast, the reaction of 1 and monocarborane [arachno-6-CB9H14]−[Et4N]+ (3) proceeds more selectively with the formation of the only one product, a isocloso-structured metallacarborane. The structures of two ruthenacarboranes were resolved by X-ray diffraction.

Stable exo-nido-Metallacarboranes (M = OsIV) that Incorporate meta-Carborane-Based Dicarbollide Ligands

Reactions of the [K]+ salts of the [nido-7,9-C2B9H12]- anion (2) and its C-phenylated derivative [7-Ph-nido-7,9-C2B9H11]- (4) with [OsCl2(PPh3)3] (3) proceed in benzene at ambient temperature with the formation of 16-electron chlorohydrido-Os(IV) exo-nido complexes, [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(mu-H)2-7-R-7,9-C2B9H8] (5: R = H; 6: R = Ph), along with the small amounts of the charge-compensated nido-carboranes [nido-7,9-C2B9H11PPh3] (7) and [7-Ph-nido-7,9-C2B9H10PPh3] (8) as byproducts. However, when carried out under mild heating in ethanol, the reaction of 2 with 3 selectively afforded a 16-electron dihydrido-Os(IV) exo-nido complex [exo-nido-10,11-{(Ph3P)2OsH2}-10,11-(mu-H)2-7,9-C2B9H9] (9). Structures of both complexes 5 and 9 have been confirmed by single-crystal X-ray diffraction studies, which revealed that nido-carboranes in these species function as a bidentate dicarbollide ligands [7-R-nido-7,9-C2B9H10]2- linked to the Os(IV) center via two B-H...Os bonds involving adjacent B-H vertices in the upper CBCBB belt of the carborane cage. Thus, compounds 5 and 9 represent the first structurally characterized exo-nido-metallacarboranes based on meta-dicarbollide-type ligands. Variable-temperature 1H and 31P{1H} NMR experiments indicate that complex 9 is fluxional in solution and shows an unusual exchange between terminal Os-(H)2 and bridging {B-H}2...Os hydrogen atoms. Upon heating in d8-THF at 65 degrees C, complex 9 converts irreversibly to its closo isomer [2,2-(PPh3)2-2,2-H2-closo-2,1,7-OsC2B9H11] (13), which could thus be obtained as a pure crystalline solid. The structure of 13 has been established on the basis of analytical and multinuclear NMR data and a single-crystal X-ray diffraction study.

Synthesis and Characterization of Novel Monocarbollide exo-closo-(π-Arene)biruthenacarboranes [(PPh3)mClRu(η6-C6H5R)Ru‘CB10H11-n(OMe)n] (where R = H, m = 2, n = 1; R = μ-PPh2, m = 1, n = 0, 1)

The monocarbon carborane [Cs][nido-7-CB(10)H(13)] reacts with the 16-electron [RuCl(2)(PPh(3))(3)] in a solution of benzene/methanol in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine as the base to give a series of 12-vertex monocarbon arene-biruthenacarborane complexes of two types: [closo-2-[7,11-exo-RuClPPh(3)(mu,eta(6)-C(6)H(5)PPh(2))]-7,11-(mu-H)(2)-2,1-RuCB(10)H(8)R] (5, R = H; 6, R = 6-MeO; 7, R = 3-MeO) and [closo-2-(eta(6)-C(6)H(6))-10,11,12-[exo-RuCl(PPh(3))(2)]-10,11,12-(mu-H)(3)-2,1-RuCB(10)H(7)R(1)] (8a, R(1) = 6-MeO; 8b, R(1) = 3-MeO, inseparable mixture of isomers) along with trace amounts of 10-vertex mononuclear hypercloso/isocloso-type complexes [2,2-(PPh(3))(2)-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(7)] (9) and [2,5-(Ph(3)P)-2-Cl-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(6)] (10). Binuclear ruthenacarborane clusters of both series were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of three selected complexes, 6-8. In solution, isomers 8a,b have been shown to undergo the isomerization process through the scrambling of the exo-[RuCl(PPh(3))(2)] fragment about two adjacent triangular cage boron faces B(7)B(11)B(12) and B(8)B(9)B(12).

Synthesis, NMR, and X-ray crystallographic analysis of C-hydrazino-C-carboxycarboranes: versatile ligands for the preparation of BNCT and BNCS agents and (99m)Tc radiopharmaceuticals

Protected hydrazine derivatives of ortho-, meta-, and para-carboranes were synthesized in good to excellent yields by reacting the mono-lithio salts of the respective carboranes with di-tert-butyl azodicarboxylate (DBAD). Subsequent deprotonation of the remaining carborane CH group, followed by the addition of CO(2)(g), resulted in the formation of bifunctional C-hydrazino-C-carboxycarboranes in good to excellent overall yields. Crystal structures of the monosubstituted ortho-carborane, 1-[(N,N'((tert-butyloxy)carbonyl)hydrazino)]-1,2-dicarba-closo-dodecaborane (8) [a = 21.213(6) A, b = 10.498(3) A, c = 9.866(2) A, alpha = gamma = 90 degrees, beta = 90.529(4) degrees ] and the bifunctional para-carborane 1-[(N,N'((tert-butyloxy)carbonyl)hydrazino)]-1,12-dicarba-closo-dodecaborane-12-carboxylic acid (3) [a = 12.744(10) A, b = 12.875(9) A, c = 14.767(9) A, alpha = beta = gamma = 90 degrees ] were obtained. Intermolecular hydrogen bonding was a dominant packing feature in both structures. The reported compounds represent a unique class of bifunctional carboranes that can be used in peptidomimetic research and as synthons to prepare novel radiopharmaceuticals and boron neutron capture therapy/boron neutron capture synovectomy (BNCT/BNCS) agents.

The Reagent [K(18-crown-6)][RuH(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))] as a Precursor to New Ruthenacarborane Complexes

In ethanol the charge-compensated molecule exo-nido-ruthenacarborane [5,6,10-{RuCl(PPh(3))(2)}-5,6,10-&mgr;-(H)(3)-10-H-7,8-C(2)B(9)H(8)] reacts with KOH to afford the anionic closo-complex [RuH(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))](-) isolated as its K(+) (2a) or [K(18-crown-6)](+) (2b) salt. Treatment of 2a with CO gives [Ru(CO)(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))] (3a) in high yield; its structure was determined by X-ray crystallography. In contrast 2b reacts with CO to yield the salt [K(18-crown-6)][RuH(CO)(PPh(3))(eta(5)-7,8-C(2)B(9)H(11))] (2d). Reaction of 2b with [RuCl(2)(PPh(3))(3)] affords [Ru(2)(&mgr;-H)(H)(PPh(3))(4)(eta(5)-7,8-C(2)B(9)H(11))] (5), which with CO produces [Ru(2)(&mgr;-H)(&mgr;-sigma: eta(5)-7,8-C(2)B(9)H(10))(CO)(4)(PPh(3))(2)] (6), the structure of which was established by X-ray diffraction. The molecule has a metal-metal bond bridged on one side by a hydrido ligand and on the other by a nido-7,8-C(2)B(9)H(10) fragment. The latter is eta(5)-coordinated to a ruthenium atom ligated by a PPh(3) and a CO ligand and is also sigma-bonded to the second ruthenium which carries three CO molecules and a PPh(3) group. The sigma bond utilizes a boron lying in an alpha site with respect to the carbons in the ring coordinated to the Ru(CO)(PPh(3)) moiety. Reactions between 2b or 2d and [CuCl(PPh(3))(3)] and [AuCl(PPh(3))], respectively, afford the bimetal complexes [RuM(&mgr;-H)(L)(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))] [M = Cu, L = PPh(3) (7a), L = CO (7b); M = Au, L = PPh(3) (8a), L = CO (8b)]. X-ray diffraction studies are reported for 7a and 8a, revealing in the case of the former a structure in which an exopolyhedral B-Hright harpoon-up Cu bond supplements the Ru(&mgr;-H)Cu interaction.