Monocarbaborane anion chemistry. [COOH], [CH2OH] and [CHO] units as functional groups on ten-vertex monocarbaborane anionic compounds

B(10)H(14) reacts with para-C(6)H(4)(CHO)(COOH) in aqueous KOH solution to give the [nido-6-CB(9)H(11)-6-(C(6)H(4)-para-COOH)](-) anion 1, which undergoes cage closure with iodine in alkaline solution to give the [closo-2-CB(9)H(9)-2-(C(6)H(4)-para-COOH)](-) anion 2. Upon heating, anion 2 rearranges to form the [closo-1-CB(9)H(9)-1-(C(6)H(4)-para-COOH)](-) anion 3. Similarly, B(10)H(14) with glyoxylic acid OHCCOOH in aqueous KOH gives the [arachno-6-CB(9)H(13)-6-(COOH)](-) anion 4, which undergoes cage closure with iodine in alkaline solution to give the [closo-2-CB(9)H(9)-2-(COOH)](-) anion 5. Upon heating, anion 5 rearranges to give the [closo-1-CB(9)H(9)-1-(COOH)](-) anion 6. Reduction of the [COOH] anions 3 and 6 with diisobutylaluminium hydride gives the [CH(2)OH] hydroxy anions [closo-1-CB(9)H(9)-1-(C(6)H(4)-para-CH(2)OH)](-) and [closo-1-CB(9)H(9)-1-(CH(2)OH)](-) 8 respectively. The [closo-1-CB(9)H(9)-1-(C(6)H(4)-para-CH(2)OH)](-) anion 7 can also be made via isomerisation of the [closo-2-CB(9)H(9)-2-(C(6)H(4)-para-CH(2)OH)](-) anion 9, in turn obtained from the [nido-6-CB(9)H(11)-6-(C(6)H(4)-para-CH(2)OH)](-) anion 10, which is obtained from the reaction of B(10)H(14) with terephthaldicarboxaldehyde, C(6)H(4)-para-(CHO)(2), in aqueous KOH solution. Oxidation of the hydroxy anions 7 and 8 with pyridinium dichromate gives the aldehydic [closo-1-CB(9)H(9)-1-(C(6)H(4)-para-CHO)](-) anion 11 and the aldehydic [closo-1-CB(9)H(9)-1-(CHO)](-) anion 12 respectively, characterised as their 2,4-dinitrophenylhydrazone derivatives, the [closo-1-CB(9)H(9)-1-C(6)H(4)-para-CH=N-NHC(6)H(3)(NO(2))(2)](-) anion 13 and the [closo-1-CB(9)H(9)-1-CH=N-NHC(6)H(3)(NO(2))(2)](-) anion respectively.     

Synthesis of nickel-monocarbollide complexes by oxidative insertion

Treatment of the 11-vertex carborane anion [closo-2-CB(10)H(11)](-) with Ni(0) reagents in tetrahydrofuran (THF) affords-via oxidative insertion reactions-12-vertex Ni(II) complexes, isolated as the salts [N(PPh(3))(2)][2,2-L(2)-closo-2,1-NiCB(10)H(11)] (L = CO (1a), CNBu(t) (1b), and CNXyl (1c; Xyl = C(6)H(3)Me(2)-2,6); L(2) = cod (1d; cod = 1,2:5,6-eta-cyclo-octa-1,5-diene)). One CO ligand in 1a is readily replaced by donors L' in the presence of Me(3)NO to give the species [N(PPh(3))(2)][2-CO-2-L'-closo-2,1-NiCB(10)H(11)] (L' = PEt(3) (1e), PPh(3) (1f), CNBu(t) (1g), and CNXyl (1h)). The anionic complexes themselves readily react with hydride abstracting reagents in the presence of donor ligands to yield zwitterionic complexes in which boron vertexes bear substituents that are bound through C, N, or O atoms. Thus, for example, 1c with H(+) and CNXyl gives [2,2,7-(CNXyl)(3)-closo-2,1-NiCB(10)H(10)] (2b), while 1f with Me(+) in the presence of OEt(2) affords [2-CO-2,11-{mu-PPh(2)(C(6)H(4)-o)}-7-OEt(2)-closo-2,1-NiCB(10)H(9)] (4), in which an additional cycloboronation of one phosphine phenyl ring has occurred. In contrast, 1f with Me(+) in the presence of NCMe gives a mixture of the isomers [2-CO-2-PPh(3)-7-{(X)-N(Me)=C(H)Me}-closo-2,1-NiCB(10)H(10)] (X identical with E (5c) and Z (5d)). X-ray diffraction analyses of compounds 1a, 2b, 4, and 5c confirmed their important structural features.     

Polyhedral monocarbaborane chemistry. Some C-phenylated seven, eight, nine, ten, eleven and twelve-vertex species

Some synthetic and structural systematics for monocarbaboranes, using the C-phenylated motif as the example, are investigated. The 10-vertex [6-Ph-nido-6-CB(9)H(11)](-) anion 1, from reaction of PhCHO with B(10)H(14) in KOH/H(2)O, is a useful entry synthon into C-phenyl monocarbaborane chemistry. Treatment of anion 1 with Na/thf yields the 10-vertex [1-Ph-closo-1-CB(9)H(9)](-) anion 2a, whereas treatment of anion 1 with iodine in alkaline solution yields the isomeric 10-vertex [2-Ph-closo-2-CB(9)H(9)](-) anion 2b, which isomerises quantitatively to 2a on heating under reflux in DME. Thermolysis of anion 1 yields the 9-vertex [4-Ph-closo-4-CB(8)H(8)](-) anion 5, whereas treatment of anion 1 with FeCl(3)/HCl gives neutral 9-vertex [4-Ph-arachno-4-CB(8)H(13)] 3. Compound 3 gives neutral 9-vertex [1-Ph-nido-1-CB(8)H(11)] 4 in refluxing toluene, and gives the 7-vertex [2-Ph-closo-2-CB(6)H(6)](-) anion 7 and the 8-vertex [1-Ph-closo-1-CB(7)H(7)](-) anion 6 in refluxing toluene with NEt(3). Reaction of 1 with [BH(3)(thf)] yields the 11-vertex [7-Ph-nido-7-CB(10)H(12)](-) anion 8 which can be converted to the 12-vertex [1-Ph-closo-1-CB(11)H(11)](-) anion 10 using [BH(3)(SMe(2))]; alternatively, anion 1 yields anion 10 directly on treatment with [BH(3)(NEt(3))]. Treatment of anion 8 with I(2)/KOH yields the 11-vertex [2-Ph-closo-2-CB(10)H(10)](-) anion 9. The structures of anions 1, 2a, 2b, 5, 6, 7, 8, 9 and 10 have been established by single-crystal X-ray diffraction analyses of their [NEt(4)](+) salts, and those of neutral 3 and 4 estimated by DFT calculations at the B3LYP/6-31G* level; similar calculations have also been applied to the new anionic closo species 2a, 2b, 5, 6, 7, 9 and 10. Crystals of the [NEt(4)](+) salt of the [2-Ph-closo-2-CB(6)H(6)](-) anion 7 required synchrotron X-radiation for sufficient diffraction intensity for molecular-structure elucidation. The syntheses are in principle generally applicable to give extensive derivative C-aryl and C-alkyl chemistries.     

Borane reaction chemistry. Alkyne insertion reactions into boron-containing clusters. Products from the thermolysis of [6,9-(2-HC[triple bond]C-C5H4N)2-arachno-B10H12

The stirring of [ortho-(HC[triple bond]C)-C(5)H(4)N] with [nido-B(10)H(14)] in benzene affords [6,9-{ortho-(HC[triple bond]C)-C(5)H(4)N}(2)-arachno-B(10)H(12)] 1 in 93% yield. In the solid state, 1 has an extended complex three-dimensional structure involving intramolecular dihydrogen bonding, which accounts for its low solubility. Thermolysis of 1 gives the known [1-(ortho-C(5)H(4)N)-1,2-closo-C(2)B(10)H(11)] 2 (13%), together with new [micro-5(N),6(C)-(NC(5)H(4)-ortho-CH(2))-nido-6-CB(9)H(10)] 3 (0.4%), [micro-7(C),8(N)-(NC(5)H(4)-ortho-CH(2))-nido-7-CB(10)H(11)] (0.4%) , 4 binuclear [endo-6'-(closo-1,2-C(2)B(10)H(10))-micro-(1(C),exo-6'(N))-(ortho-C(5)H(4)N)-micro-(exo-8'(C),exo-9'(N))-(ortho-(CH(2)CH(2))-C(5)H(4)N)-arachno-B(10)H(10)] (0.5%) 5, and [exo-6(C)-endo-6(N)-(ortho-(CH[double bond]CH)-C(5)H(4)N)-exo-9(N)-(ortho-(HC[triple bond]C)-C(5)H(4)N)-arachno-B(10)H(11)] 6. An improved solvent-free route to 2 is also presented. This set of compounds features an increasing cluster incorporation of the ethynyl moiety, initially by an effective internal hydroboration, affording an arachno to nido and then a nido to arachno:closo sequence of cluster geometry. An alternative low-temperature route to internal hydroboration is demonstrated in the room temperature reaction of [closo-B(11)H(11)][N(n)Bu(4)](2) with CF(3)COOH and [ortho-(HC[triple bond]C)-C(5)H(4)N], which gives [micro-1(C),2(B)-[ortho-C(5)H(4)N-CH(2)]-closo-1-CB(11)H(10)] 7 (40%) in which one carbon atom is incorporated into the cluster; a similar reaction with [ortho-(N[triple bond]C)-C(5)H(4)N] affords [N(n)Bu(4)][7-(ortho-N[triple bond]C-C(5)H(4)N)-nido-B(11)H(12)], 8 (68%) and stirring [ortho-(N[triple bond]C)-C(5)H(4)N] with [nido-B(10)H(14)] quantitatively affords the cyano analogue of 1, [6,9-{ortho-(N[triple bond]C)-C(5)H(4)N}(2)-arachno-B(10)H(12)] 9. All compounds were characterised by single-crystal X-ray diffraction analysis and NMR spectroscopy.     

Transmission of electronic effects through the {closo-1-CB9} and {closo-1-CB11} cages: apparent dissociation constants for series of [closo-1-CB9H8-1-COOH-10-X] and [closo-1-CB11H10-1-COOH-12-X] acids

The apparent ionization constants pK(a)' for series of carboxylic acids [closo-1-CB(9)H(8)-1-COOH-10-X](-) (1) and [closo-1-CB(11)H(10)-1-COOH-12-X](-) (2), where X = H, I, n-C(6)H(13), (+)NMe(3), (+)N(2), (+)SMe(2), OC(5)H(11), were measured in EtOH/H(2)O (1/1, v/v) at 24 °C. Correlation analysis of the pK(a)' values using Hammett substituent constants σ(p)(X) gave the reaction constant ρ = 0.87 ± 0.04 for series 1 and ρ = 1.00 ± 0.09 for series 2. These values are higher than for derivatives of PhCH═CHCOOH (ρ = 0.70 ± 0.09 in 55% EtOH) and correspond to 56% and 65% efficiencies in transmission of electronic effects by [closo-1-CB(9)H(10)](-) (E) and [closo-1-CB(11)H(12)](-) (F), respectively, as compared to benzene (A). Experimental results were supported with DFT calculations of relative acidity for series of acids derived from A, E, and F in aqueous medium.     

Unusual interaction of alkynes with nine-vertex arachno-monocarbaboranes 4-CB8H14 and [4-CB8H13]-

Alkynes R(1)R(2)C(2) react with the neutral monocarbaborane arachno-4-CB(8)H(14) (1) at elevated temperatures (115-120 degrees C) under the formation of the derivatives of the ten-vertex dicarbaborane nido-5,6-C(2)B(8)H(12) (2) of general formula 9-Me-5,6-R1,R2-nido-5,6-C(2)B(8)H(9) (where R1,R2 = H,H 2a; Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph 2e) in moderate yields (26-52%). Side reaction with PhC(2)H also yields 1-Ph-6-Me-closo-1,2-C(2)B(8)H(8) (3d). In contrast, the reaction between [arachno-4-CB(8)H(13)](-) anion ((-)) and PhC(2)H produces a mixture of the closo anions [1-CB7H8]- (4-) and [1-CB6H7]- (5-) (yields 32 and 24%, respectively). Individual compounds were isolated and purified by liquid chromatography and characterized by NMR spectroscopy ((11)B, (1)H and (13)C) combined with two-dimensional [(11)B-(11)B]-COSY and (1)H-{(11)B(selective)}NMR techniques.     

Alkyne coupling at a rhenium-monocarborane substrate: synthesis of Re,B-eta2:sigma-butadienyl complexes

Treatment of 7-NH(2)Bu(t)-nido-7-CB(10)H(12) in tetrahydrofuran (THF) with LiBu(n)(3 equiv) and then [ReBr(CO)(3)(THF)(2)] gives the rhenacarborane dianion [1-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)](2-), isolated as the bis-[N(PPh(3))(2)](+) salt (4). Iodine oxidation of this Re(I) intermediate gives the Re(III) complex [1,2-mu-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)] 6 in which the carborane functions formally as an 8-electron (6pi+ 2sigma) donor. Reaction of with ligands L in the presence of Me(3)NO gives substituted products [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-closo-2,1-ReCB(10)H(10)][L = PPh(3)(7a), CNXyl (7b; Xyl = C(6)H(3)Me(2)-2,6), or Bu(t)C triple bond CH (7c)]. Formation of complex 7c is unexpectedly accompanied by [1,2-mu-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)] 8a, in which an alkyne-derived dienyl group is bound to both the rhenium centre and to an adjacent boron vertex. Complex 8a is also obtained from 7c with Bu(t)C triple bond CH and Me(3)NO. The same reaction of 7c, using PhC triple bond CH or CNXyl instead of Bu(t)C triple bond CH, gives, respectively, [1,2-micro-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHPh}-closo-2,1-ReCB(10)H(9)] 8b and [1,2-micro-NHBu(t)-2-Bu(t)C triple bond CH-2-CO-2-CNXyl-closo-2,1-ReCB(10)H(10)] 9. Addition of donors L to results in displacement from rhenium of the pendant dienyl moiety, yielding [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-3-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)][L = PMe(3)(10a), CNBu(t)(10b)]. Single-crystal X-ray diffraction analyses have confirmed the novel structural features of compounds 6, 7c, 8b and 9.     

Preparation of 1-p-halophenyl and 1-p-biphenylyl substituted monocarbadodecaborate anions [closo-1-Ar-CB11H11]- by insertion of arylhalocarbenes into [nido-B11H14]-

In the presence of a strong base, benzal chloride (C(6)H(5)CHCl(2)) and its p-substituted derivatives react with [nido-B(11)H(14)](-) to yield [closo-1-p-X-C(6)H(4)-CB(11)H(11)](-) (X = H, F, Cl, Br, I, Ph), presumably by insertion of an arylhalocarbene and oxidation. On a 1-g scale, the yields are 30-40%, except in the case of p-iodobenzal chloride, which yields only 12% of the insertion product.     

Unprecedented cage-carbon to cage-boron NMe(3) transfer in a monocarbon Molybdenacarborane

The reagent Li(2)[7-NMe(3)-nido-7-CB(10)H(10)] reacts with [Mo(CO)(3)(NCMe)(3)] in THF-NCMe (THF = tetrahydrofuran) to give a molybdenacarborane intermediate which, upon oxidation by CH(2)[double bond]CHCH(2)Br or I(2) and then addition of [N(PPh(3))(2)]Cl, gives the salts [N(PPh(3))(2)][2,2,2-(CO)(3)-2-X-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (X = Br (1) or I (2)). During the reaction, the cage-bound NMe(3) substituent is transferred from the cage-carbon atom to an adjacent cage-boron atom, a feature established spectroscopically in 1 and 2, and by X-ray diffraction studies on several of their derivatives. When [Rh(NCMe)(3)(eta(5)-C(5)Me(5))][BF(4)](2) is used as the oxidizing agent, the trimetallic compound [2,2,2-(CO)(3)-7-mu-H-2,7,11-[Rh(2)(mu-CO)(eta(5)-C(5)Me(5))(2)]-closo-2,1-MoCB(10)H(9)] (10) is formed, the NMe(3) group being lost. Reaction of 1 in CH(2)Cl(2) with Tl[PF(6)] in the presence of donor ligands L affords neutral zwitterionic compounds [2,2,2-(CO)(3)-2-L-3-NMe(3)-closo-2,1-MoCB(10)H(10)] for L = PPh(3) (4) or CNBu(t) (5), and [2-Bu(t)C[triple bond]CH-2,2-(CO)(2)-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (6) when L = Bu(t)C[triple bond]CH. When 1 is treated with CNBu(t) and X(2), the metal center is oxidized, and in the products obtained, [2,2,2,2-(CNBu(t))(4)-2-Br-3-X-closo-2,1-MoCB(10)H(10)] (X = Br (7), I (8)), the B-NMe(3) bond is replaced by B-X. In contrast, treatment of 2 with I(2) and cyclo-1,4-S(2)(CH(2))(4) in CH(2)Cl(2) results in oxidative substitution of the cluster and retention of the NMe(3) group, giving [2,2,2-(CO)(3)-2-I-3-NMe(3)-6-[cyclo-1,4-S(2)(CH(2))(4)]-closo-2,1-MoCB(10)H(9)] (9). The unique structural features of the new compounds were confirmed by single-crystal X-ray diffraction studies upon 6, 7, 9 and 10.     

Substitution, cage functionalization, and oxidation of the charge-compensated triruthenium monocarbollide cluster complex [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8

The compound [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8] 1a reacts with PMe3 or PCy3(Cy = cyclo-C6H11) to give the structurally different species [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)5(PMe3)}-closo-2,1-RuCB10H8] 4 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)5(PCy3)}-closo-2,1-RuCB10H8]5, respectively. A symmetrically disubstituted product [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)4(PMe3)2}-closo-2,1-RuCB10H8] 6 is obtained using an excess of PMe3. In contrast, the chelating diphosphines 1,1'-(PPh2)2-Fe(eta-C5H4)2 and 1,2-(PPh2)2-closo-1,2-C2B10H10 react with 1a to yield oxidative-insertion species [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(micro-[1',1'-(PPh2)2-Fe(eta-C5H4)2])(CO)4}-closo-2,1-RuCB10H8] 7 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)4(1',2'-(PPh2)2-closo-1',2'-C2B10H10)}-closo-2,1-RuCB10H8] 8, respectively. In toluene at reflux temperatures, 1a with Bu(t)SSBu(t) gives [1-SMe2-2,2-(CO)2-7-(mu-SBu(t))-11-(mu-H)-2,7,11-{Ru2(mu-H)(mu-SBu(t))(CO)4}-closo-2,1-RuCB10H8] 9, and with Bu(t)C [triple bond] CH gives [1-SMe2-2,2-(CO)2-7-{mu:eta2-(E)-CH=C(H)Bu(t)}-11-{mu:eta2-(E)-CH=C(H)Bu(t)}-2,7,11-{Ru2(CO)5}-closo-2,1-RuCB10H8] 10. In the latter, two alkyne groups have inserted into cage B-H groups, with one of the resulting B-vinyl moieties involved in a C-H...Ru agostic bond. Oxidation of 1a with I2 or HgCl2 affords the mononuclear ruthenium complex [1-SMe2-2,2,2-(CO)3-closo-2,1-RuCB10H10] 11.     

Carba-closo-dodecaborates with one or two alkynyl substituents bonded to boron

Salts of the carba-closo-dodecaborate anion with one or two phenyl- or trimethylsilylalkynyl substituents were synthesized by Pd-catalyzed Kumada-type cross-coupling reactions of the corresponding iodinated clusters with alkynyl Grignard reagents. Selective monofunctionalization in the 7- and 12-position of the {closo-CB(11)} cluster was achieved, resulting in salts of the anions: [1-R-12-R'C[triple bond]C-closo-CB(11)H(10)](-) (R = H, Ph; R' = Ph, Me(3)Si (1-4)), [12-Hal-7-PhC[triple bond]C-closo-CB(11)H(10)](-) (Hal = F (5), Cl (6), Br (7)), and [12-F-7-Me(3)SiC[triple bond]C-closo-CB(11)H(10)](-) (8). Furthermore, the disubstituted derivatives [7,12-(RC[triple bond]C)(2)-closo-CB(11)H(10)](-) (R = Ph (9), Me(3)Si (10)) are described. All salts were characterized by multi-NMR, IR, and Raman spectroscopy as well as by mass spectrometry (MALDI). The crystal structures of Cs(+)1 and [Et(4)N](+)6 were determined by single-crystal X-ray diffraction. The spectroscopic and structural properties are compared to values derived from DFT calculations and to data of related boron species with alkynyl groups.     

New palladium-catalyzed cross-coupling routes to carbon functionalized metallatricarbadecaboranes

A general method for the synthesis of cage-carbon-functionalized cyclopentadienyl iron and cyclopentadienyl ruthenium tricarbadecaboranyl complexes has been developed that employs palladium-catalyzed Sonogashira, Heck, and Stille cross-coupling reactions directed at a cage-carbon haloaryl substituent. The key Li(+)[6-(p-XC(6)H(4))-nido-5,6,9-C(3)B(7)H(9)(-)] (X = I (1), Br (2), Cl (3)) haloaryl-tricarbadecaboranyl anionic ligands were synthesized in high yields via the reaction of the arachno-4,6-C(2)B(7)H(12)(-) anion with the corresponding p-halobenzonitriles (p-XC(6)H(4)-CN). The reactions of the salts 1-3 with (η(5)-C(5)H(5))Fe(CO)(2)I and (η(5)-C(5)H(5))Ru(CH(3)CN)(3)PF(6) were then used to produce the haloaryl complexes 1-(η(5)-C(5)H(5))-2-(p-XC(6)H(4))-closo-1,2,3,4-MC(3)B(7)H(9) (M = Fe, X = I (4), Br (5), Cl (6) and M = Ru, X = I (7), Br (8), Cl (9)). The sonication-promoted Sonogashira coupling reactions of 4 with terminal alkynes catalyzed by Pd(dppf)(2)Cl(2)/CuI yielded the alkynyl-linked derivatives 1-(η(5)-C(5)H(5))-2-p-RC(6)H(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (R = (PhC≡C)- (10), (CH(3)CH(2)C(O)OCH(2)C≡C)- (11), ((η(5)-C(5)H(5))Fe(η(5)-C(5)H(4)C≡C))- (12)). Heck reactions of 4 with terminal alkenes catalyzed by Pd(OAc)(2) yielded the alkene-functionalized products 1-(η(5)-C(5)H(5))-2-p-RC(6)H(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (R = (PhCH(2)CH═CH)- (13), (CH(3)(CH(2))(2)CH═CH)- (14)), while the Stille cross-coupling reactions of 4 with organotin compounds catalyzed by Pd(PPh(3))(2)Cl(2) afforded the complexes 1-(η(5)-C(5)H(5))-2-p-RC(6)H(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (R = Ph- (15), (CH(2)═CH)- (16), (CH(2)═CHCH(2))- (17)). These reactions thus provide facile and systematic access to a wide variety of new types of functionalized metallatricarbadecaboranyl complexes with substituents needed for potential metallocene-like biomedical and/or optoelectronic applications.     

Syntheses of functionalized ferratricarbadecaboranyl complexes

The reactions of nitriles (RCN) with arachno-4,6-C(2)B(7)H(12)(-) provide a general route to functionalized tricarbadecaboranyl anions, 6-R-nido-5,6,9-C(3)B(7)H(9)(-), R = C(6)H(5) (2(-)), NC(CH(2))(4) (4(-)), (p-BrC(6)H(4))(Me(3)SiO)CH (6(-)), C(14)H(11) (8(-)), and H(3)BNMe(2)(CH(2))(2) (10(-)). Further reaction of these anions with (eta(5)-C(5)H(5))Fe(CO)(2)I yields the functionalized ferratricarbadecaboranyl complexes 1-(eta(5)-C(5)H(5))-2-C(6)H(5)-closo-1,2,3,4-FeC(3)B(7)H(9) (3), 1-(eta(5)-C(5)H(5))-2-NC(CH(2))(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (5), 1-(eta(5)-C(5)H(5))-2-[(p-BrC(6)H(4))(Me(3)SiO)CH]-closo-1,2,3,4-FeC(3)B(7)H(9) (7), 1-(eta(5)-C(5)H(5))-2-C(14)H(11)-closo-1,2,3,4-FeC(3)B(7)H(9) (9), and 1-(eta(5)-C(5)H(5))-2-H(3)BNMe(2)(CH(2))(2)-closo-1,2,3,4-FeC(3)B(7)H(9) (11). Reaction of 11 with DABCO (triethylenediamine) resulted in removal of the BH(3) group coordinated to the nitrogen of the side chain, giving 1-(eta(5)-C(5)H(5))-2-NMe(2)(CH(2))(2)-closo-1,2,3,4-FeC(3)B(7)H(9) (12). Crystallographic studies of complexes 3, 5, 7, 9, and 11 confirmed that these complexes are ferrocene analogues in which a formal Fe(2+) ion is sandwiched between the cyclopentadienyl and tricarbadecaboranyl monoanionic ligands. The metals are eta(6)-coordinated to the puckered six-membered face of the tricarbadecaboranyl cage, with the exopolyhedral substituents bonded to the low-coordinate carbon adjacent to the iron.     

Synthesis, structure, and dynamics of nickelacarboranes incorporating the [nido-7,9-C(2)B(9)H(11)](2)(-) ligand

The nickelacarboranes [NEt(4)][2-(eta(3)-C(3)H(4)R)-closo-2,1,7-NiC(2)B(9)H(11)] (R = H (1a), Ph (1b)) have been synthesized via reaction between [Na](2)[nido-7,9-C(2)B(9)H(11)] and [Ni(2)(micro-Br)(2)(eta(3)-C(3)H(4)R)(2)] in THF (THF = tetrahydrofuran), followed by addition of [NEt(4)]Cl. Protonation of 1a in the presence of a donor ligand L affords the complexes [2,2-L(2)-closo-2,1,7-NiC(2)B(9)H(11)] (L = CO (2), CNBu(t) (3)). Addition of PEt(3) (1 equiv) to 2 produces quantitative conversion to [2-CO-2-PEt(3)-closo-2,1,7-NiC(2)B(9)H(11)], 4. Species 2-4 exhibit in solution hindered rotation of the NiL(2) fragment with respect to the eta(5)-C(2)B(9) cage unit. Protonation of 1a in the presence of a diene affords the neutral complexes [2-(eta(2):eta(2)-diene)-closo-2,1,7-NiC(2)B(9)H(11)] (diene = C(5)Me(5)H (5), dcp (6), cod (7), nbd (8), chd (9), and cot (10a); dcp = dicyclopentadiene, cod = 1,5-cyclooctadiene, nbd = norbornadiene, chd = 1,3-cyclohexadiene, and cot = cyclooctatetraene). Variable temperature (1)H NMR experiments show that the [Ni(diene)] fragments are freely rotating even at 193 K. A small quantity of the di-cage species [2,2'-micro-(1,2:5,6-eta-3,4:7,8-eta-cot)-(closo-2,1,7-NiC(2)B(9)H(11))(2)] (10b) is formed as a coproduct in the synthesis of 10a. This species can be rationally synthesized by protonation of 1a and subsequent addition of 10a.     

Ten-vertex iron-monocarbollide complexes: synthesis and reactivity of the anion [4,9-{Fe(CO)4}-9,9,9-(CO)3-arachno-9,6-FeCB8H11]-

The reagent [arachno-4-CB8H14] reacts with [Fe3(CO)12] in tetrahydrofuran (THF) at reflux temperatures, followed by addition of [N(PPh3)2]Cl, to afford [N(PPh3)2][4,9-{Fe(CO)4}-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (3). In the anion of 3, one iron atom is part of the open CBBFeBB face of a 10-vertex {arachno-9,6-FeCB8} cage, to which the second iron atom is attached via an Fe-Fe bond and an additional exo-polyhedral Fe-B sigma bond. Upon heating 3 in refluxing toluene, the closed 10-vertex species [N(PPh3)2][2,2,2-(CO)3-closo-2,1-FeCB8H9] (4) is obtained, whereas the isomeric compound [N(PPh3)2][6,6,6-(CO)3-closo-6,1-FeCB8H9] (5) is isolated upon heating [closo-4-CB8H9]- and [Fe3(CO)12] in refluxing THF with subsequent addition of [N(PPh3)2]Cl. Protonation of 3 using CF3SO3H in CH2Cl2 gives the charge-compensated compound [4,9-{Fe(CO)4}-4-(mu-H)-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (6), in which the B-Fe sigma bond of the precursor has been converted to a B-H right harpoon-up Fe linkage. In contrast, 3 with {M(PPh3)}+ gives the trimetallic species [1,3,4,9-{MFe(CO)4(PPh3)}-1,3-(mu-H)2-9,9,9-(CO)3-arachno-9,6-FeCB8H9] (M = Cu (7), Ag 8) in which the three metal centers form a V-shaped M-Fe-Fe unit. Compound 6 reacts with PEt3 in the presence of Me(3)NO to yield [4,9-(PEt3)2-9,9-(CO)2-nido-9,6-FeCB8H10] (9). In the latter, the formerly exo-polyhedral {Fe(CO)4} fragment has been replaced by a PEt3 ligand, with a second PEt3 substituting one CO group at the remaining cluster iron vertex. The novel structural features of compounds 3-9 have been confirmed by single-crystal X-ray diffraction studies.     

Silver phosphanes partnered with carborane monoanions: synthesis, structures and use as highly active Lewis acid catalysts in a hetero-Diels-Alder reaction

Four Lewis acidic silver phosphane complexes partnered with [1-closo-CB(11)H(12)](-) and [1-closo-CB(11)H(6)Br(6)](-) have been synthesised and studied by solution NMR and solid-state X-ray diffraction techniques. In the complex [Ag(PPh(3))(CB(11)H(12))] (1), the silver is coordinated with the carborane by two stronger 3c-2e B-H-Ag bonds, one weaker B-H-Ag interaction and a very weak Ag.C(arene) contact in the solid state. In solution, the carborane remains closely connected with the [Ag(PPh(3))](+) fragment, as evidenced by (11)B chemical shifts. Complex 2 [Ag(PPh(3))(2)(CB(11)H(12))](2) adopts a dimeric motif in the solid state, each carborane bridging two Ag centres. In solution at low temperature, two distinct complexes are observed that are suggested to be monomeric [Ag(PPh(3))(2)][CB(11)H(12)] and dimeric [Ag(PPh(3))(2)(CB(11)H(12))](2). With the more weakly coordinating anion [CB(11)H(6)Br(6)](-) and one phosphane, complex 3 [Ag(PPh(3))(CB(11)H(6)Br(6))] is isolated. Complex 4, [Ag(PPh(3))(2)(CB(11)H(6)Br(6))], has been characterised spectroscopically. All of the complexes have been assessed as Lewis acids in the hetero-Diels-Alder reaction of N-benzylideneaniline with Danishefsky's diene. Exceptionally low catalyst loadings for this Lewis acid catalysed reaction are required (0.1 mol %) coupled with turnover frequencies of 4000 h(-1) (quantitative conversion to product after 15 minutes using 3 at room temperature). Moreover, the reaction does not occur in rigorously dry solvent as addition of a substoichiometric amount of water (50 mol %) is necessary for turnover of the catalyst. It is suggested that a Lewis assisted Br?nsted acid is formed between the water and the silver. The effect of changing the counterion to [BF(4)](-), [OTf](-) and [ClO(4)](-) has also been studied. Significant decreases in reaction rate and final product yield are observed on changing the anion from [CB(11)H(6)Br(6)](-), thus demonstrating the utility of weakly coordinating carborane anions in organic synthesis.     

Monocarbaborane anion chemistry. The elusive C-arylated [PhCB11H11]-, [PhCB9H9]- and [PhCB8H8]- anions

B10H14 and PhCHO yield [6-Ph-nido-6-CB9H11]- (94%), from which the nine-vertex C-phenyl monocarbaborane anion [4-Ph-closo-4-CB8H8]- (68%) can be obtained by heating at 200 degrees C, and from which the twelve- and ten-vertex analogues [1-Ph-closo-1-CB11H11]- (50%) and [4-Ph-closo-4-CB9H9]- (25%) can be obtained by heating at 210 degrees C with BH3(NEt3).     

Reductive degradation of nido-1-CB8H12 into smaller-cage carborane systems via new monocarbaboranes [arachno-5-CB8H13](-) and closo-2-CB6H8

Treatment of the nido-1-CB8H12 (1) carborane with NaBH4 in THF at ambient temperature led to the isolation of the stable [arachno-5-CB8H13]- (2(-)), which was isolated as Na+[5-CB8H13]-.1.5 THF and PPh4 +[5-CB8H13]- in almost quantitative yield. Compound 2(-) underwent a boron-degradation reaction with concentrated hydrochloric acid to afford the arachno-4-CB7H13 (3) carborane in 70 % yield, whereas reaction between 2(-) and excess phenyl acetylene in refluxing THF gave the [closo-2-CB6H7]- (4-) in 66 % yield. Protonation of the Cs+4(-) salt with concentrated H2SO4 or CF3COOH in CH2Cl2 afforded a new, highly volatile 2-CB6H8 (4) carborane in 95 % yield, the deprotonation of which with Et3N in CH2Cl2 leads quantitatively to Et3NH+[2-CB6H7](-) (Et3NH+4(-)). Both compounds 4- and 4 can be deboronated through treatment with concentrated hydrochloric acid in CH2Cl2 to yield the carbahexaborane nido-2-CB5H9 (5) in 60 % yield. New compounds 2-, 3, and 4 were structurally characterised by the ab initio/GIAO/MP2/NMR method. The method gave superior results to those carried out using GIAO-HF when relating the calculated 11B NMR chemical shifts to experimental data.     

Penta- and hexaruthenium carbonyl 'raft' complexes supported by monocarborane cage ligands

Reaction between [PPh4][closo-4-CB8H9] and [Ru3(CO)12] in refluxing toluene affords the unprecedented hexaruthenium metallacarborane salt [PPh4][2,3,7-{Ru(CO)3}-2,6,11-{Ru(CO)3}-7,11,12-{Ru(CO)3}-3,6,12-(micro-H)3-2,2,7,7,11,11-(CO)6-closo-2,7,11,1-Ru3CB8H6] (1a), which contains a planar Ru6 'raft' supported by a {CB8} monocarborane cluster. Addition of [CuCl(PPh3)]4 and Tl[PF6] to a CH2Cl2 solution of 1a results in simple cation replacement, forming the analogous [Cu(PPh3)3]+ salt (1b). The phenyl-substituted monocarborane [NEt4][6-Ph-nido-6-CB9H11] reacts with [Ru3(CO)12] in refluxing 1,2-dimethoxyethane to afford the pentaruthenium cluster species [N(PPh3)2][2,3,7-{Ru(CO)3}-3,4,8-{Ru(CO)3}-7,8-(micro-H)2-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H6] (2), after addition of [N(PPh3)2]Cl. Treatment of 2 with [CuCl(PPh3)]4 and Tl[PF6] in CH2Cl2 forms the zwitterionic complex [10,12-{exo-Cu(PPh3)2}-2,3,7-{Ru(CO)3}-3,4,8-{Ru(CO)3}-7,8,10,12-(micro-H)4-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H4] (3). Substitution of CO by PPh3 with concomitant cation replacement occurs on introduction of [AuCl(PPh3)], Tl[PF6], and PPh3 to a CH2Cl2 solution of 2, forming [Au(PPh3)2][2,3,7-{Ru(CO)2PPh3}-3,4,8-{Ru(CO)2PPh3}-7,8-(micro-H)2-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H6] (4). Crystallographic studies confirmed the cluster architectures in 1b, 2, and 3.     

OCO and NCO chelated derivatives of heavier group 15 elements. Study on possibility of cyclization reaction via intramolecular ether bond cleavage

A set of four pincer ligands, either the OCO type ligands L(1-3) [2,6-(ROCH(2))(2)C(6)H(3)](-), where R = Me (L(1)), mesityl (L(2)), t-Bu (L(3)) or novel NCO ligand [2-(Me(2)NCH(2))-6-(t-BuOCH(2))C(6)H(3)](-) was studied. The reaction of L(4)Li with PCl(3) resulted in isolation of [2-(OCH(2))-6-(Me(2)NCH(2))C(6)H(3)]PCl (1) as a result of intramolecular ether bond cleavage and elimination of t-BuCl. The conversion between the organolithium compounds L(1,2,4)Li and AsCl(3) led to the desired chlorides, i.e. (L(1))(2)AsCl (2), L(2)AsCl(2) (3), L(4)AsCl(2) (5), but an analogous reaction using the L(3)Li compound gave [2-(OCH(2))-6-(t-BuOCH(2))C(6)H(3)]AsCl (4) as a result of intramolecular cyclization. The organoantimony chloride L(3)SbCl(2) was shown to undergo very slow cyclization in CDCl(3) again via elimination of t-BuCl giving [2-(OCH(2))-6-(t-BuOCH(2))C(6)H(3)]SbCl (6) and it was demonstrated that this reaction may be accelerated by preparation of L(3)Sb(Cl)(OTf) (7) with more Lewis acidic central atom. On the contrary, both antimony derivatives of the NCO ligand L(4), not only the chloride L(4)SbCl(2) (8) but also the ionic pair containing highly Lewis acidic cation [L(4)SbCl](+)[CB(11)H(12)](-) (9), are stable without any indication for etheral bond cleavage. The situation is rather similar in the case of organobismuth derivatives of L(4), which allowed isolation of compounds L(4)BiCl(2) (10), L(4)Bi(Cl)(OTf) (11) and [L(4)BiCl](+)[CB(11)H(12)](-) (12). All studied compounds were characterized by the help of (1)H and (13)C NMR spectroscopy, ESI mass spectrometry, elemental analysis and (except 1) by single-crystal X-ray diffraction.