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The reaction of [Na][C2B8H11] with anhydrous FeCl2 in THF affords a mixture of DD/LL and MESO isomers of anionic paramagnetic commo-ferracarborane [Ph3PR][commo-1,1′-Fe(closo-2,4-C2B8H10)2] (MESO, R = Me: 1a; MESO, Et: 1b; DD/LL, R = Me: 2a; DD/LL, R = Et: 2b) with unusual closo geometry. Both: DD/LL and MESO isomers were successfully isolated and their structures were determined using X-Ray diffraction studies. Paramagnetic properties were confirmed with EPR-spectra as well as oxidative-reductive properties were investigated using cyclic voltammetry. It was shown that facile DD/LL → MESO and MESO → DD/LL transformation leading to equilibrium in CH2Cl2 solution occurs. Quantum chemical calculations of the isomer-to-isomer transformations were performed. Ferra-copper zwitterionic complexes [3,3′,6,7′-exo-{Ph3PCu}-3,3′,6,7′-(µ-H)4-commo-1,1′-Fe(2,4-C2B8H8)2] and [3,3′,6,6′-exo-{Ph3PCu}-3,3′,6,6′-(µ-H)4-commo-1,1′-Fe(2,4-C2B8H8)2] were synthesized and their structures were determined by X-Ray diffraction studies.

Treatment of a recently reported complex [Ph4P][closo,nido-CoH(2,4-C2B8H10)(7,8-C2B8H11)] (1) either by H2O2 in acetone or NaH in THF leads to the loss of both the bridging and terminal hydrides yielding the diamagnetic salt of an anionic commo-cobaltacarborane [Ph4P][Co(2,4-isonido-C2B8H10)2] (2) with the {CoC2B8}-cluster units adopting a distorted skeletal geometry of the isonido-type. The anionic commo complex 2 reacts with in situ generated cationic [CuPPh3]+ species to give stable copper–cobalt zwitterion [Ph3PCu][Co(2,4-isonido-C2B8H10)2] (3) with four two-electron, three-center (B–H)4···Cu bonds, and exhibits no fluxional behavior in solution. Complex 3, at the same time, in CH2Cl2 in the presence of 2-fold excess of PPh3 readily converts to a new anionic species [(Ph3P)3Cu][Co(2,4-isonido-C2B8H10)2] (4) which retains initial isonido geometry. All newly obtained diamagnetic commo complexes were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crysta...

An experimentally based and theoretical electron density study of the title compound has been carried out, giving the first experimental description for the two types of bonding: between the transition metal (i.e., Co) and the dicarbollide dianions that occurs through the open C2B3 face of the nido-carborane and between the anionic commo cluster (i.e., Cobdc) and the transition metal (i.e., Cu) involving three unique (B–H)3···Cu bonds. The Co···dicarbollide and Cu···Cobdc bonds are shown to have a multicenter character, whereas direct Co···Cu interaction is found to be absent. The effect of the [Cu(PPH3)]+ association with the Cobdc anion on the Co···dicarbollide bonding is discussed. The description of intramolecular Co···dicarbollide and intermolecular B–H···H–C connectivity in terms of the Hirshfeld approach and Voronoi tessellation is compared with the QTAIM results to confirm their qualitative and semiquantitative similarity.

Quantum chemical calculations were carried out for exo-nido - and closo -ruthenacarborane clusters containing phosphine and diphosphine ligands. The calculated energies and geometric parameters of the complexes show that closo -ruthenacarboranes with seven- or eight-membered ω-diphosphaalkyl-substituted ruthenacycles are the most stable compounds in the studied series. The results explain the effect of the nature of the diphosphine ligand on the reactivity and catalytic activity of the ruthenacarboranes in ATRP processes.

The reaction of the middle-cage carborane 5,6-nido-C2B8H12 with the dimeric rhodium complexes [(η2-C8H14)2RhCl]2 or [(η4-C8H12)RhCl]2 in a MeOH/C6H6 mixture gave the anionic commo-rhodacarborane [PPN][commo-1,1′-Rh(isonido-2,4-C2B8H10)2] (as a mixture of meso and dd/ll isomers) and its 7-B-methoxylated derivative [PPN][commo-1,1′-Rh(7-MeO-isonido-2,4-C2B8H9)(isonido-2,4-C2B8H10)] in moderate yields. The latter was subjected to the thermal isonido-to-closo rearrangement to form the new commo-cluster [PPN][commo-1,1′-Rh(closo-2,3-C2B8H9OMe)(closo-2,3-C2B8H10)]. The newly synthesized compounds were characterized by NMR spectroscopy and X-ray diffraction.

The heating of a mixture of 14-e [Ph2P(CH2)nPPh2]FeCl2 (n = 3 or 2) with the [K]+ salt of the [nido-7,8-C2B9H12]− mono-anion under gentle reflux in benzene affords either the paramagnetic (17-electron) complex [3,3-(dppp)-3-Cl-closo-3,1,2-FeC2B9H11] isolated in 15% yield or a mixture of the paramagnetic complex [3,3-(dppe)-3-Cl-closo-3,1,2-FeC2B9H11] (46% yield) and the diamagnetic complex [commo-8,8′-μ-(Ph2PCH2CH2PPh2)-3,3′-Fe{1,2-C2B9H10}2] (10% yield). All three novel ferracarboranes were characterized by spectroscopic (EPR or NMR) data and single-crystal X-ray diffraction.

A reaction of anhydrous CuCl2 with Na salts of the medium-cage carborane [7-X-nido-5,6-C2B8H10]−(X = H or I) derivatives in THF leads to new cupracarborane commo-clusters, [commo-9,9′-Cu(nido-7,8-C2B8H11)2]− and [commo-9,9′-Cu(11-I-nido-7,8-C2B8H10)2]−, in moderate yields. The clusters were isolated as stable [Ph3PEt]+ salts and characterized by 1H, 31P{1H}, and 11B/11B{1H} NMR spectroscopy and X-ray crystallography (for the unsubstituted derivative). The use in this reaction of the reducing agent Na2SO3 considerably increases the yields of both complexes from 25 and 18% to 74 and 68%, respectively.

Reactions of [ exo -5,6,10-{Cl(Ph 3 P) 2 Ru}-5,6,10-(μ-H) 3 -10-H- nido -7,8-C 2 B 9 H 8 ] ( 1 ) with 1,5-bis(diphenylphosphino)pentane ( 2 ) in benzene either at ambient temperature for ca 2 days or under gently reflux for 30 min in anaerobic conditions both proceed with the replacement of PPh 3 ligands on the ruthenium center with the diphosphine to form diamagnetic (18-electron) closo complex [3,3-{κ 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Cl-3-H- closo -3,1,2-RuC 2 B 9 H 11 ] ( 3 ). On heating in benzene, 3 in the presence of a small amount of CCl 4 affords stable paramagnetic (17-electron) species [3,3-{κ 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Cl- closo -3,1,2-RuC 2 B 9 H 11 ] ( 5 ) along with traces of ortho -phenylenecycloboronated closo complex, ( 7 ). The latter complex was prepared in higher yields by thermal treatment of either 3 or 5 under more severe conditions in toluene at 110 °C. Thermolysis of 7 in boiling toluene in the presence of a small amount of CCl 4 afforded the new paramagnetic complex ( 8 ), featuring bis( ortho -cycloboronation) of both P-phenyl groups located at the same phosphorus atom of the ruthenium bound dppt ligand; a minor amount of chloro-cage-substituted complex ( 9 ) was also isolated from the latter reaction as the by-product. All new closo -ruthenacarboranes obtained were characterized by a combination of analytical, multinuclear NMR (for even-electron species) or EPR (for odd-electron species) data and, in addition, by single-crystal X-ray diffraction studies of three paramagnetic complexes 5 , 7 and 8 .

The reaction of the ruthenacarborane exo - nido -5,6,10-[Cl(Ph 3 P) 2 Ru]-5,6,10-(m-H) 3 -10-H-7,8-(Ph) 2 -7,8-C 2 B 9 H 6 with phenylacetylene in dichloromethane in the presence of triethylamine at ambient temperature affords exo - nido -5,6,10-[(Ph 3 P) 2 Ru]-5,6-(μ-H) 2 -10-[μ-(PhC=CH)]-10-H-7,8-(Ph) 2 -7,8-C 2 B 9 H 6 containing vinylene bridge group between carborane framework and ruthenium atom. Structure of the complex has been determined by X-ray diffraction study.

Reactions of [3,3-(PPh3)2-3-Cl-3-H-3,1,2-closo-RuC2B9H11] (1) and its exo-nido isomer [exo-5,6,10-{Ru(Ph3P)2Cl}-5,6,10-(μ-H)3-10-H-7,8-nido-C2B9H8] (2) with NH4PF6 in methanol or ethanol solution followed by heating in the presence of an excess of phenylacetylene (3) affords a mixture of two isomeric closo species [3,3-{(1′-3′-η3):(5′,6′-η2)-ortho-C6H4PPh2CHC(Ph)CHCHPh}-8-(σ–CH CHPh)-3,1,2-closo-RuC2B9H10] (4) and [3,3-{(1′-3′-η3):(5′,6′-η2)-ortho-C6H4PPh2CHC(Ph)CHCHPh}-4-(σ–CH CHPh)-3,1,2-closo-RuC2B9H10] (5) in which boron vertexes in β- and α-sites with respect to the cage carbons bear the (E)–CH CHPh group. The X-ray diffraction study of 4 together with the multinuclear NMR data for 4 and 5 revealed that such an unusual η3:η2-phosphacarbocyclic ligand in both isomeric complexes is formed by specific insertion of the initially metal-bound PPh3 group into the chain of two alkyne molecules coupled in a “head-to-tail” fashion around the metal vertex.

Reaction of the mononuclear complex [3-{(1-3)-η3-C8H13}-1,2-(CH3)2-3,1,2-IrC2B9H9] (1) with air or oxidizing reagent (C6H5CO2)2 unexpectedly produces μ,η-COD-ligated biiridacarboranes [Ir(η1,η5-1,n...

The room temperature reactions between [Rh2(η5-C5Me5)2Cl4] (1) and [K][7-R1-8-R2-7,8-nido-C2B9H10] (2a–d: a, R1 = R2 = H; b, R1 = R2 = Me; c, R1 = H, R2 = PhCH2; d, R1 = R2 = PhCH2) in solution of C6H6–EtOH mixture (4:1) to give [3-(η5-C5Me5)-1-R1-2-R2-3,1,2-closo-RhC2B9H9] (3a–d), respectively, have been shown to proceed through the formation of the first step ionic intermediates of the type [(η5-C5Me5)Rh(μ-Cl)3Rh(η5-C5Me5)][7-R1-8-R2-7,8-nido-C2B9H10] (4a–d). All ionic compounds 4a–d were isolated in the solid state and characterized by a combination of analytical, IR and multinuclear NMR data, including a single-crystal X-ray diffraction study of 4d. The structure of 3d (R1 = R2 = PhCH2), the first 12-vertex closo-type metallacarborane species bearing sterically demanding C,C′-dibenzylsubstituted carborane ligand, has also been determined by an X-ray crystallography.

Reactions of the [K]+ salt of the [7,8-(4‘-MeC6H4)2-7,8-nido-C2B9H10]- monoanion with the COD−rhodium and COD−iridium μ-chloride complexes [(η4-COD)2M2(μ-Cl)2] proceed in benzene at ambient temperature with the formation of the 16-electron complexes [3-{(1−3-η3)-C8H13}-1,2-(4‘-MeC6H4)2-3,1,2-pseudocloso-MC2B9H9] (5, M = Rh(III); 6, M = Ir(III)), respectively, whose pseudocloso strucrure has been confirmed by single-crystal X-ray diffraction studies. The major species 5 is formed along with a small amount of the dimeric rhodacarborane [(η6-MeC6H4)Rh(C2B9H9C6H4Me)Rh(η4-C8H12)]2 (7), which, as found from X-ray structure determinations, is composed of two distorted {4,9,1,10-Rh2C2B9} cluster units joined together through η6 coordination of the 4-tolyl cage substituent of one unit to one of the rhodium atoms of the second unit and vice versa.

Reactions of [ exo-nido -5,6,10-{Cl(Ph 3 P) 2 Ru}-5,6,10-(μ-H) 3 -10-H-7,8-R 2 -7,8-C 2 B 9 H 6 ] ( 1 , R = H; 2 , R = Me) with the chiral (2S,4S)-2,4-bis(diphenylphosphino)pentane ( 3 , S , S -bdpp) ligand proceed in benzene with replacement of both PPh 3 ligands on the metal center with the diphosphine affording the chelate exo-nido complexes [ exo-nido -5,6,10-{Cl( S , S -bdpp)Ru}-5,6,10-(μ-H) 3 -10-H-7,8-R 2 -7,8-C 2 B 9 H 6 ] ( 7 , R = H) and ( 8 , R = Me), respectively. A relatively fast and irreversible rearrangement of 7 into its closo isomer [ closo -3,3-( S , S -bdpp)-3-Cl-3-H-3,1,2-RuC 2 B 9 H 11 ] ( 4 ) occurs in solution already at room temperature. On the contrary, exo-nido -to- closo conversion of 8 proceeds in benzene (or much faster in toluene) only on heating and yields 17-electron paramagnetic complex [ closo -3,3-( S , S -bdpp)-3-Cl-1,2-Me 2 -3,1,2-RuC 2 B 9 H 9 ] ( 9 ). All exo-nido - and closo -ruthenacarboranes obtained were characterized by a combination of analytical, multinuclear NMR or EPR spectroscopic data and, in addition, by X-ray diffraction studies of both dimethylated complexes 8 and 9 .

The replacement of the PPh3 ligands in “three-bridge” exo-nido-ruthenacarborane 5,6,10-[RuCl(PPh3)2]-5,6,10-(µ-H)3-10-H-exo-nido-7,8-C2B9H8 with diphosphines, viz., 1,3-bis(diphenylphosphino)propane (dppp) or 1,4-bis(diphenylphosphino)butane (dppb) dramatically decreases the barrier to the thermal exo-nido→closo rearrangement affording the chelate closo-complexes 3,3-[Ph2P(CH2)nPPh2]-3-H-3-Cl-closo-3,1,2-RuC2B9H11 (n = 3 or 4) under mild conditions. In the reaction with dppp, the rearrangement is accompanied by the formation of 17-electron paramagnetic closo-ruthenacarborane 3,3-[Ph2P(CH2)3PPh2]-3-Cl-closo-3,1,2-RuC2B9H11, which could be isolated as the main product when the reaction was carried out at 80 °C.

Treatment of [exo-nido-{Cl(Ph3P)2Ru}-μ-(H)3-10-H-7,8-C2B9H8] (1) with the (2S,4S)-(−)-2,4-bis(diphenylphosphino)pentane (3, BDPP) while heating in toluene results in the formation of three novel optically active diphosphine–ruthenium closo complexes, 18e diamagnetic (−)-[closo-3-Cl-3,3-{(S,S)-BDPP}-3-H-3,1,2-RuC2B9H11] (4), and 17e paramagnetic (−)-[closo-3-Cl-3,3-{(S,S)-BDPP}-3,1,2-RuC2B9H11] (5) along with its ortho-cycloboronated derivative (−)-[closo-3-Cl-3,3-{(S,S)-Ph2PCH(CH3)CH2CH(CH3)PPh- (6). Both odd-electron complexes 5 and 6 were characterized by single-crystal X-ray diffraction analysis.

A reaction of complexes CoCl2(dppe) (dppe is the 1,2-bis(diphenylphosphino)ethane) or CoCl2(dppp) (dppp is the 1,3-bis(diphenylphosphino)propane) with [K][7,8-nido-C2B9H12] upon reflux in benzene led to the mixed ligand closo-cobaltacarboranes [3,3-(Ph2P(CH2) n PPh2)-3-Cl-closo-3,1,2-CoIIIC2B9H11] (n = 2 and 3, respectively) in moderate yields (34 and 16%). The structure of the 18-electron complexes in solution and the solid state was studied by NMR and IR spectroscopy, the structure in the case of the closo-complex with dppe-ligand was confirmed by X-ray crystallography.

The mixed-ligand di-m-chloro-bridged rhodium dimers [(?2-C8H14)(?4-2-methylbuta-1,3-diene)Rh(µ-Cl)]2 and [(?2-C8H14)(?4-2,3- dimethylbuta-1,3-diene)Rh(µ-Cl)]2 were synthesized and characterized. These compounds are key precursors in the preparative syn- thesis of the acyclic (p-allyl)-closo-rhodacarborane complexes [3-{p-(R”-allyl)}-1-R-2-R’-closo-3,1,2-RhC2B9H9], which were obtained earlierviathe one-pot metallation of the K+ salts of the [7-R-8-R’-nido-7,8-C2B9H10]– anions with [(?2-C8H14)4Rh2(µ-Cl)2] in the presence of substituted buta-1,3-diene ligands.

Agostic (C−H···M) complexes [closo-3,3-(σ,η2-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-IrC2B9H9] (5) and [closo-3,3-(σ,η2-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-RhC2B9H9] (9), stable in the solid state, have been prepared via the reaction of [M(η4-COD)Cl]2 (M = Ir, Rh) with the K+ salt of the [nido-7,8-μ-(ortho-xylylene)-7,8-C2B9H10]- anion and characterized by a combination of analytical (in the case of 5) and multinuclear NMR data, including a single-crystal X-ray diffraction study of 5. The crystallographic study confirmed the agostic structure of 5 and revealed that the orientation of the σ,η2-cyclooctenyl moiety relative to the carborane ligand is substantially influenced by the specific intramolecular C−H···π interaction between the agostic hydrogen and the π-system of the cage aromatic substituent. In solution, 5 exhibited both “side-to-side” agostic hydrogen migration and reversible interconversion with [closo-3-(η3-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-IrC2B9H9] (8). The agostic rhodium complex (9), in cont...

The reactions of a complex [(η4-C7H8)RhCl]2 (C7H8 is norbornadiene) with salts of substituted nido-dicarbaundecaborates, [K][nido-7-R1-8-R2-7,8-C2B9H10] (R1 = R2 = H (a); R1 = R2 = Me (b); R1, R2 = 1′,2′-(CH2)2C6H4 (c); R1 = Me, R2 = Ph (d)), in CH2Cl2 afforded new closo-(η2,η3-(4-vinylcyclopenten-3-yl))rhodacarboranes. The structures of the compounds were studied by multinuclear NMR spectroscopy. A probable mechanism of the rearrangement of the norbornadiene ligand is discussed.

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).

Reactions of [OsCl2(PPh3)3] 1 with the [NEt4]+ salts of the [6-Ph-nido-6-CB9H11]− anion 2 and the [arachno-6-CB9H14]− anion 3 each proceed selectively in methanol solution with the elimination of one boron-containing fragment from the starting cluster polyhedron, yielding together a short series of three novel 10-vertex hydridoosmamonocarbaboranes of isocloso {OsCB8} cluster geometry.

Heating of 1,1,3-(PPh3)3-1-H-1,2,4-RuC2B8H9 with 2-(hydroxymethyl)bicyclo[2.2.1]hepta-2,5-diene in arene solvents (benzene, toluene, or mesitylene) unexpectedly afforded the ruthenium arene complexes 1-(η6-arene)-3-(C7H9CH2O)-isonido-1,2,4-RuC2B8H9 containing the nortricyclene fragment in the carborane ligand.

A series of arene-ruthenium 11-vertex complexes 3-Cl-1-(η6-arene)-isonido-1,2,4-RuC2B8H9 (4a-4h) and 6-Cl-1-(η6-arene)-isonido-1,2,4-RuC2B8H9 (5a, 5b, 5f, 5g) (arene = p-xylene (a), mesitylene (b), p-cymene (c), benzene (d), toluene (e), hexamethylbenzene (f), 1,2,4,5-tetramethylbenzene (g), 1,2,4-trimethylbenzene (h)) have been obtained as isomeric mixtures 4a, 4b, 4f, 4g and 5a, 5b, 5f, 5g or, predominantly, as single isomers 4c-4e, 4h by the treatment of nido-5,6-C2B8H12 (1) with [RuCl2(PPh3)3] (2), either in the corresponding arene solvents at 80-85 °C (in the case of 4a-4e and 5a, 5b) or in the arene/1,2-dichloroethane solution under reflux (in the case of 4f-4h and 5f, 5g) in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine. The compounds prepared were characterized by combination of analytical, IR and multinuclear NMR data, including a crystallographic study of 4b. A possible pathway for the formation of isomeric complexes 4 and 5 is discussed.

The reactions of agostic (CH3···Rh) complexes [3-{(1-3-η(3))-1,1,2-trimethylallyl}-1-R-2-R'-closo-3,1,2-RhC2B9H9] [1: R = R' = Me; 2: R,R' = μ-(ortho-xylylene); 3: R = Ph, R' = Me] in a cooled (+5 °C) toluene solution with the strong non-nucleophilic base N,N,N',N'-tetramethylnaphthalene-1,8-diamine (tmnd) formally involve a linear coupling of the π-allyl ligand of one molecule of the complex to the π-allyl ligand of the second molecule of the complex, ultimately forming the structurally novel mononuclear species [3-{(1-5-η(5))-2,3-dimethyl-5-(3-methylbuten-2-yl)pentadienyl}-1-R-2-R'-closo-3,1,2-RhC2B9H9] (4, 5) and (6a,b, a mixture of diastereomers). Complexes 5 and 6a,b were also prepared using weaker bases such as PPh3 or even EtOH instead of tmnd. All new complexes 4-6 were characterized by a combination of analytical and multinuclear NMR data, as well as by single-crystal X-ray diffraction studies of two selected species 5 and the major diastereomer of 6, which revealed an open η(5)-pentadienyl coordination mode of the hydrocarbon ligands in these complexes.

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4-Hg)3 (1) is capable of binding closo-[B10H10]2- and closo-[B12H12]2- anions to form complexes [[(o-C6F4Hg)3](B10-H10)]2- (2), [[(o-C6F4Hg)3]2(B10H10)]2-(3), [[(o-C6F4Hg)3](B12H12)]2- (4), and [[(o-C6F4Hg)3]2(B12H12)]2- (5). According to IR data, the bonding of the [B10H10]2- and [B12H12]2- ions to the macrocycle in these complexes is accomplished through the formation of B-H-Hg bridges. Complexes 2, 3, and 5 have been isolated in analytically pure form and have been characterized by spectroscopic means. X-ray diffraction studies of 3 and 5 have revealed that these compounds have unusual sandwich structures, in which the polyhedral di-anion is located between the planes of two molecules of 1 and is bonded to each of them through two types of B-H-Hg bridges. One type is the simultaneous coordination of a B-H group to all three Hg atoms of the macrocycle. The other type is the coordination of a B-H group to a single Hg atom of the cycle. According to X-ray diffraction data, complex 2 has an analogous but half-sandwich structure. The obtained complexes 2-5 are quite stable; their stability constants in THF/acetone (1:1) at 20 degrees C have been determined as 1.0 x 10(2)Lmol(-1), 2.6 x 10(3)L(2)mol(2), 0.7 x 10(2)Lmol(-1), and 0.98 x 10(3)L(2)mol(-2), respectively.

A series of diastereomeric closo-(η1,2-dicyclopentenyl)rhodacarborane complexes with the agostic C--H...Rh bond were synthesized starting from mono-C-substituted anionic nido-carboranes [nido-7-R-7,8-C2B9H11]–. The resulting diastereomeric mixtures were separated into individual isomers by either crystallization or chromatography. The structures and the stereochemistry of the diastereomeric complexes were studied in detail by 1H and 13C NMR spectroscopy. The relative configurations of two key isomers were established by X-ray diffraction analysis. The mechanism of the stereospecific formation of diastereomeric complexes is discussed.

The reaction of OsCl2(PPh3)3 with [nido-7-R1-8-R2-C2B9H10]K+ produced a series of new exo-nido-osmacarborane complexes exo-nido-5,6,10-[Cl(Ph3P)2Os]-5,6,10-(μ-H)3-10-H-7-R1-8-R2-7,8-C2B9H6 (1: R1 = R2 = H; 2: R1 = R2 = Me; 3: R1 = R2 = PhCH2; 4: R1 + R2 = 1,2-C6H4(CH2)2; 5: R1 = H, R2 = Me) in which the osmium-containing group is linked to the nido-carborane ligand through three two-electron three-center bonds. Compounds 1—5 are formed as mixtures of symmetric (a) and asymmetric (b) isomers; pure symmetric isomers 2a and 4a were isolated by fractional crystallization, and the mixture of isomers 3a, was quantitatively separated into individual compounds 3a and 3b by column chromatography on silica gel. Detailed analysis of the 31P{1H}, 1H, 11B NMR spectra of 1a,b—5a,b and 2D 1H-1H{11B} and 11B{1H}-11B{1H} NMR spectra of 3a and 3b was performed. The structures of isomers 2a and 4a were confirmed by an X-ray diffraction study. According to the NMR and X-ray diffraction data, the isomerism of exo-nido-complexes 1a,b—5a,b is actually the cis—trans-isomerism of ligand arrangement in the octahedral coordination of the Os atom.

A facile ligand-exchange method based on the direct reaction of either three-bridge exo-nido complex [exo-5,6,10-{Cl(Ph3P)2Ru}- 5,6,10-(μ-H)3-10-H-nido-7,8-C2B9H8] or its closo isomer [3,3-(PPh3)2-3-Cl-3-H-3,1,2-closo-RuC2B9H11] with chelating N,N-donor ligands was employed to synthesize the N,N-diamine-closo-ruthenacarborane complexes [3,3-{κ2-4,4’-R2-2,2’-(C5H3N)2}-3-PPh3-closo-3,1,2-RuC2B9H11] (R = H, But) and [3,3-{κ2-phen}-3-PPh3-closo-3,1,2-RuC2B9H11].

The reaction of exo-nido-5,6,10-[Cl(PPh3)2Ru]-5,6,10-(μ-H)3-10-H-7,8-C2B9H8) (1) with [(η4-diene)RhCl]2 in EtOH or with [(CO)2RhCl]2 in MeOH in the presence of KOH produced novel mixed-metal bimetallacarboranes (η4-diene)Rh(μ-H)Ru(PPh3)2(η5-C2B9H11) (4, diene = COD; 5, diene = NBD) or (CO)(PPh3)Rh(μ-H)Ru(PPh3)2(η5-C2B9H11) (10) along with a small amount of the mononuclear complexes closo-(CO)2(PPh3)Ru(η5-C2B9H11) and closo-(CO)(PPh3)2Ru(η5-C2B9H11), respectively. Complexes 4 and 10 were characterized by single-crystal X-ray diffraction studies which revealed the existence of two types of bridging bonds Ru−H−Rh and B−H···Rh in these species. The bridging hydrogen atoms are asymmetrically disposed within these linkages. Several separate experiments have been carried out for the synthesis of the anionic complex [closo-3,3-(PPh3)2-3-H-3,1,2-RuC2B9H11]-, which is proposed to be the key intermediate in the reaction of 1 with [(η4-diene)RhCl]2. The reaction of (PPh3)3RuHCl with [7,8-C2B9H12][Me3NH] under reflux ...

The first η2-olefinic monocarbon metallacarbone closo-2-(Ph3P)-1-N,2-[μ-(η2-CH2CHCh2)]-1-N-(σ-CH2CHCH2)-2,1- RhCB10H10 has been prepared by the reaction of the dimeric anion {[Ph3PRhB10H10CNH2]2-μ-H}−[PPN]+ with allyl bromide and characterized by a combination of spectroscopic methods and a single-crystal X-ray diffraction study. The variable temperature 1H and 13C NMR studies revealed the fluxional behavior of the η2-olefinic complex in CD2Cl2 solution which is associated with the allyl side-chain exchange process.

A model has been developed that allows one to carry out molecular mechanics calculations of metallacarborane complexes with various ligands with the use of the MM3 program package. Based on X-ray structural data on a number of rhodium complexes in which the rhodium atom is coordinated by the η2,3-norbornadienyl and η5-dicarbollyl ligands, a parameter set was developed for the compounds of the above-mentioned series. The use of this model made it possible to study the effects of various factors on the structures of the molecules ofcloso-3,3-(η2,3-methylenenorbornadienyl)-1-R-3, 1,2-dicarbollylrhodium (R=Alk or ArAlk).

The catalytic reduction of the exocyclic methylene group of methacycline (A) leads to the formation of two diastereoisomers, doxycycline (B, the α-epimer) and 6-epi-doxycycline (C, the β-epimer), with a selectivity which markedly depends on the nature of hydrocarbon and carborane ligands of closo-(π-cyclodienyl)rhodacarborane catalysts. Neutral norbornadienyl complexes with unsubstituted carborane ligands [closo-3,3-(η2,3-C7H7CH2)-3,1,2-RhC2B9H11] (1) and [closo-2,2-(η2,3-C7H7CH2)-2,1,7-RhC2B9H11] (7) are more active and afford higher selectivity in the formation of doxycycline than those having mono- or di-substituents at the carborane cage, [closo-3,3-(cyclodienyl)-1-R-2-R′-3,1,2-RhC2B9H9] (R = H, R′ = Me, PhCH2; R = R′ = Me; cyclodienyl = η2,3-C7H7CH2 or η-C10H13) as well as those from the closely related series of η5-cyclopentadienyl complexes [(η2,3-C7H7CH2)Rh(η5-C5Rn)]+PF6− (Rn = H5, Me5, or H2-1,2,4-Ph3). Mechanistic aspects of the hydrogenation reaction of methacycline are sketched. The results of the X-ray diffraction study of the best catalyst 1 are reported.

Novel 12-vertex closo-hydridometallacarboranes 3,1,2-[(PPh3)2OsHXC2B9H11] (1a,b: X = Cl, H) and 3,1,2-[(PPh3)2OsH2-1,2-Me2C2B9H9] (1c) have been synthesized via oxidative addition of K+ salts of the nido-carborane anions [nido-7,8-R2-7,8-C2B9H10]- (R = H, Me), respectively, to OsCl2(PPh3)3 and characterized by spectroscopic (NMR and IR) as well as by single-crystal X-ray diffraction studies of 1a,c.

A family of macrocyclic compounds are described, together with their precursors. These cycles are composed of icosahedral carboranes linked via their carbon vertices through 1,3-trimethylene, alpha,alpha'-1,3-xylylene, or alpha,alpha'-2,6-lutidylene groups. The compounds cyclo-(1,3-trimethylene-1',2'-closo-1',2'-C(2)B(10)H(10))(4) (6a), cyclo-(1,3-trimethylene-1',2'-closo-9',12'-dimethyl-1',2'-C(2)B(10)H(8))(4) (6b), cyclo-(1,3-trimethylene-1',2'-closo-1',2'-C(2)B(10)H(10))(3) (9), cyclo-(alpha,alpha'-1,3-xylylene-1',2'-closo-1',2'-C(2)B(10)H(10))(2) (11a), cyclo-(alpha,alpha'-1,3-xylylene-1',7'-closo-1',7'-C(2)B(10)H(10))(2) (11b), cyclo-(alpha,alpha'-1,3-xylylene-1',7'-closo-9',10'-dimethyl-1,7-C(2)B(10)H(8))(2) (11c), cyclo-(alpha,alpha'-1,3-xylylene-1',2'-closo-1',2'-C(2)B(10)H(10))(4) (12), cyclo-(alpha,alpha'-1,3-xylylene-1',7'-closo-1',7'-C(2)B(10)H(10))(3) (13), cyclo-(alpha,alpha'-2,6-lutidylene-1',7'-closo-1',7'-C(2)B(10)H(10))(2) (19), and cyclo-(alpha,alpha'-2,6-lutidylene N-oxide-1',7'-closo-1',7'-C(2)B(10)H(10))(2) (20) have been synthesized. The structures of 6a, 6b, 9, 11a, 11b, 11c, 12, and 19 have been determined by X-ray crystallography. Crystal data: for 6a, triclinic, space group Ponemacr;, a = 11.131(2) Å, b = 12.642(2) Å, c = 12.996(2) Å, alpha = 84.383(6) degrees, beta = 65.884(6) degrees, gamma = 97.292(5) degrees, Z = 1, R = 0.079; for 6b, monoclinic, space group P2(1)/a, a = 13.500(2) Å, b = 31.141(3) Å, c = 13.831(2) Å, beta = 99.90(1) degrees, Z = 2, R = 0.097; for 11a, monoclinic, space group C2/c, a = 14.5682(8) Å, b = 14.5046(8) Å, c = 16.1998(8) Å, beta = 95.631(2) degrees, Z = 4, R = 0.081; for 11b, monoclinic, space group P2(1)/n, a = 11.650(2) Å, b = 10.606(2) Å, c = 11.730(2) Å, beta = 104.951(6) degrees, Z = 2, R = 0.069; for 11c, orthorhombic, space group Pbca, a = 12.532(2) Å, b = 14.271(2) Å, c = 18.143(3) Å, Z = 4, R = 0.076; for 19, orthorhombic, space group Pcab (No. 61, standard setting Pbca), a = 11.0428(6) Å, b = 11.3785(6) Å, c = 22.533(1) Å, Z = 4, R = 0.074.

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.

Treatment of [nido-B10H12CH]-Cs+ with RuCl2(PPh3)3 in methanol under gentle reflux afforded the two novel 10-vertex monocarbon ruthenacarboranes 2-Cl-2,5-(Ph3P)2-2-H-3,9-(MeO)2-2,1-RuCB8H6 (3) and 2,2-(Ph3P)2-2-H-3,9-(MeO)2-2,1-RuCB8H7 (4) along with a small amount of the 8-vertex complex (PPh3)2HRuCB6H4(OMe)3 (6). The 10-vertex clusters 3 and 4 on the basis of their capped-tricapped-trigonal-prismatic geometry, established for 3 by a single-crystal X-ray diffraction study, and the formal Wadian electron-counting arguments can be regarded as hyper-closo species having n rather than n + 1 skeletal electron pairs.

Protonation of the [closo-3,3-(η4-C10H12)-1-(CH2OH)-3,1,2-RhC2B9H10]− PPN+ (C10H12 — dicyclopentadiene, PPN+ — bis(triphenylphosphine)iminium cation) at the ethylene bond of the norbornene moiety yields the neutralcloso-3,3,3-(η-C10H13)-1-(CH2OH)-3,1,2-RhC2B9H10 with an agostic C-H...Rh bond. On prolonged storage in EtOH, the latter complex is converted intocloso-3,3-(η3,2-C10H11)-1-(CH2OH)-3,1,2-RhC2B9H10 with π-allylolefinic type coordination. Its crystal structure as dimeric aggregates with O-H...O and O-H...Rh bonds was determined by X-ray diffraction.

Novel exo-nido-ruthenacarboranes, 5,6,10-[CI(Ph3P)2Ru]-5,6,10-μ-(H)3-10-H-7,8-R2C2B9H6 (1; R = H, structurally characterized by an X-ray diffraction study, and 2; R = Me) have been prepared by reaction of RuCl2 (PPh3)3 and [nido-7,8-R2C2B9H10]− K+ in diethyl ether-tetrahydrofuran; in the solid state clusters 1 and 2 contain tridentate nido–carborane ligands bound to the RuII atom through three Ru—H—B bridging hydrogen bonds, whereas in solution they exist as an equilibrium mixture of isomeric exo-nido-bis(triphenylphosphine)chlorohydridoruthenacarboranes formed as a result of the cleavage of one of the Ru—H—B bonds with the formation of a new Ru—B σ-bond and a simultaneous hydrogen atom shift to the metal atom.

The molecular structure of 8-vertex capped closo-[(Ph3P)2HRuCB6H4(OMe)3] has been elucidated by an X-ray diffraction study. The cluster features a unique RuCB6 skeleton and cage geometry which is based on a boron-capped pentagonal bipyramid. This constitutes the first reported example of metallacarboranes with an “isolated” (nonfused) polyhedron exhibiting such geometry.

The previously synthesized mixture of diastereomeric complexescloso-3,3-(η2,3-C7H7CH2)-1-(PhCH2)-3,1,2-RhC2B9H10 was separated by TLC on silica gel into individual diastereomers, whose stereochemistry and relative configurations were determined by X-ray diffraction analysis.

Treatment of (2-hydroxymethylnorbornadiene)cyclopentadienylrhodium (V) with sulfuric acid offers the stable cationic complex XI, which can be isolated as PF 6 − or BF 4 − . 1 H and 13 C NMR data indicate that in cation XI the bicyclic ligand is bound to the metal via η 2 -ethylene and η 3 -allyl bonds, including an exocyclic methylene carbon. The structure of complex XI is supported by a single-crystal X-ray diffraction study of its PF 6 − salt. Reaction of diastereomeric carbinols ψ- exo -VI and ψ- endo -Rh {η 4 -C 7 H 7 CH(OH)Me} (η 4 -C 5 H 5 ) (VII) proceeds with absolute stereospecificity to form syn -XII and anti -[Rh(η 5 -C 7 H 7 CHMe)(η 5a -C 5 H 5 )] + (XIII) isomers, respectively. Similarly, cation [Rh(η 5 -C 7 H 7 CHPh)(η 5 -C 5 H 5 )] + (XV), derived from ψ- endo -Rh {η 4 -C 7 H 7 CH(OH)Ph}(η 5 -C 5 H 5 ) (IX), has the syn configuration. However, the same reaction of the ferrocenyl-substituted carbinol ψ- endo -Rh {η 4 -C 7 H 7 CH(OH)Fc} (η 5 -C 5 H 5 ) (X) leads to mixture of two isomeric complexes, syn -(XVI) and anti -[Rh(η 5 -C 7 H 7 CHFc)(η 5 -C 5 H 5 )] + (XVII), in a ratio of 4 1 . The absolute stereospecificity and the relative facility with which the formation of cationic η 3 -allylic complexes from carbinols VI, VII and IX takes place are due to the nucleophilic participation of a rhodium atom in stabilizing the electron-deficient center during the reaction. The disturbance of stereospecificity during the conversion of carbinol X to a cationic complex assumes the formation of an α-ferrocenylcarbenium ion (XIX) as an intermediate (a product of kinetic control). Owing to the relative non-hindrance of rotation around the exocyclic carboncarbon bond C(2)—C(8) in the carbenium ion XIX, the formation of a non-equal mixture of complexes XVI and XVII, the products of thermodynamic control of the reaction, takes place.

Novel 18-electron rhodacarboranes with a 2-methylenenorbornadienyl ligand, η 2 ,η 3 -coordinated to a rhodium atom of closo-3,3-(η 2 ,η 3 -C 7 H 7 CH 2 )-1,2-R 1 R 2 -3,1,2-RhC 2 B 9 H 9 (IIIa–IIId, R 1  R 2  H (a), R 1  R 2  Me (b), R 1  Me or Ph, R 2  H (c,d) and closo-2,2-(η 2 ,η 3 -C 7 H 7 CH 2 )-2,1,7-RhC 2 B 9 H 11 (VIII) have been prepared. The structures of IIIa–IIId, and VIII were deduced from their IR, 1 H NMR and 13 C NMR spectra. Two alternative synthetic routes to the above complexes have been suggested: (a) reactionis of 16-electron complexes of (η 4 -C 7 H 7 -2-CH 2 OH)- Rh(acac) or [(η 4 -C 7 H 7 -2-CH 2 OH)RhCl] 2 with appropriate dicarbollide anions with a subsequent acidificatiion by HPF 6 and (b) reactions of unsubstituted and C-mono-substituted closo-bis(triphenylphosphine)hydridorhodacarboranes with 2-(hydroxymethyl)norbornadiene on heating in benzene. The possible mechanisms of these reactions are discussed. An X-ray study of complex IIIb, R 1  R 2  Me, confirms that there is allylolefin type metal-ligand bonding.

The cationic alkoxyallylolefin complexes of rhodium, [Rh(η 2 -5,6-η 3 -2,3,8-C 7 H 7 -2-CHOR)(η 5 -C 5 H 5 )] + An − (II) were prepared as stable salts from the reaction of Rh(η 4 -C 7 H 7 -2-CHO)(η 5 -C 5 H 5 ) (I) with ROH (R = Me, Et) in the presence of HBF 4 or HPF 6 . A preliminary X-ray study of the cation IIa (R = Me, An = PF 6 ) confirms the metal-ligand bonding of the η 2 -5,6-η 3 -2,3,8-allylolefinic type with a significant participation of the oxygen atom of the methoxy group in stabilization of the C(8) cationic centre. The above-mentioned cationic complexes were found to be key intermediates in the formation and hydrolysis of the dialkylacetals of the corresponding aldehyde.