Kenneth Wade

C-arylation and C-heteroarylation of icosahedral carboranes via their copper(I) derivatives

Abstract Reaction between C-mono- or C,C′-di-copper(1) derivatives of 1,2-, 1,7-, or 1,12-dicarba-closo-dodecaborane(12) and aryl iodides in the presence of pyridine gives the corresponding C-mono- or C,C′-diaryl derivatives of 1,7- and 1,12-dicarba-closo-dodecaboranes(12); 1,2-dicarba-closo-dodecaborane(12) gives only the C-monoaryl product. Cyclic or linear arylene coupled systems are obtained when di-iodoarenes are used. Copper(I) derivatives may be generated from C-unsubstituted or C-monosubstituted carboranes using copper(I) t-butoxide when substituents incompatible with the use of C-lithio-intermediates are involved. The C-copper(I) derivative of 1,2-dicarba-closo-dodecaborane(12) gives 1,2-di-2′-pyridyl-1,2-dicarba-closo-dodecaborane(12) specifically with 2-bromopyridine. The (inferred) intermediate mono-2-pyridyl-derivative, obtained independently from 2-ethynylpyridine and the dimethylsulphide complex of decaborane, gives 1-phenyl-2,2′-pyridyl-1,2-dicarba-closo-dodecaborane(12) upon conversion into its copper(I) derivative and treatment with iododobenzene. However, the copper(I) derivative of 1-phenyl-1,2-dicarba-closo-dodecaborane(12) does not react to a significant extent with 2-bromopyridine.

Definitive crystal structures of ortho-, meta- and para-carboranes: supramolecular structures directed solely by C–H⋯O hydrogen bonding to hmpa (hmpa = hexamethylphosphoramide)

Cocrystallisation of ortho-meta- and para-carboranes with hmpa (hexamethylphosphoramide) results in the isolation of 1 : 1 carborane:hmpa adducts which provide the first definitive X-ray structures of the unsubstituted carboranes as part of three very different C–H⋯O hydrogen-bonded supramolecular structures.

Exo-π-bonding to an ortho-carborane hypercarbon atom: systematic icosahedral cage distortions reflected in the structures of the fluoro-, hydroxy- and amino-carboranes, 1-X-2-Ph-1,2-C2B10H10 (X = F, OH or NH2) and related anions

The structures of derivatives of phenyl-ortho-carborane bearing on the second cage hypercarbon atom a pi-donor substituent (F, OH, O-, NH2, NH- and CH2-) were investigated by NMR, X-ray crystallography and computational studies. The molecular structures of these compounds, notably their cage C1-C2 distances and the orientations of their pi-donor substituents (OH, NH2, NH- and CH2-) show remarkable and systematic variations with the degree of exo pi-bonding, which varies as expected with the pi-donor characteristics of the substituent.

Deboronation of C-substituted ortho- and meta-closo-carboranes using “wet” fluoride ion solutions

Abstract Hydrated tetrabutylammonium fluoride has been found to be more effective than the anhydrous salt as a reagent for the conversion of ortho and metal closo -carborane derivatives, R′R″C 2 B 10 H 10 , into nido -carborane anions, [R′R″C 2 B 9 H 10 ] − , allowing access to a number of new nido -carborane derivatives difficult to prepare, or inaccessible, using other deboronating reagents, notably the meta -carborane derivatives, [7,9-R′R″-7,9-C 2 B 9 H 10 ] − [Bu 4 N] + (R′ = 4-HOC 6 H 4 , 4-O 2 NC 6 H 4 ; R″ = H and R′ = R″ = 4-PhOC 6 H 4 , 4-O 2 NC 6 H 4 , 2-C 5 H 4 N, 4-H 2 NC 6 H 4 ). Experiments with the bis( p -bromophenyl- ortho -carboranyl)benzene, 1,4-[4-BrC 6 H 4 CB 10 H 10 C] 2 C 6 H 4 , carried out to determine the quantity of tetrabutylammonium fluoride needed to deboronate both cages, afforded the salt 1,4-[7-(4-BrC 6 H 4 )C 2 B 9 H 10 ] 2 C 6 H 4 2− [Bu 4 N + ] 2

Fluoride-ion deboronation of p-fluorophenyl-ortho- and -meta-carboranes. NMR evidence for the new fluoroborate, HOBHF2−

Abstract The reactions of 1-(4-fluorophenyl)-1,2-dicarbadodecaborane(12) 1 and 1-(4-fluorophenyl)-1,7-dicarbadodecaborane(12) 2 with tetrabutylammonium fluoride hydrate in tetrahydrofuran or acetonitrile have been monitored by 19F and 11B NMR. No carborane intermediates were observed prior to formation of the nido- anions 7-(4-FC6H4)-7,8-C2B9H11− 3 and 7-(4-FC6H4)-7,9-C2B9H11− 4 which each required two molecular proportions of fluoride and, by inference, one of water for complete reaction. The spectra of the initial anionic monoboron product of both reactions showed it to be the new fluoroborate HOBHF2− 5. The B-attached hydrogen atom of the fluoroborate 5 is derived from the starting carborane, since it was retained when Bu4NF·(D2O)n was used, but the nido-anions 3 and 4 bonded deuterium at the open face in this experiment. The 1H, 11B, 19F and 13C NMR spectra of carboranes 1–4 have been recorded and assigned.

Deboronation of 9-substituted-ortho- and -meta-carboranes

Abstract A systematic study has been carried out of deboronation reactions of a series of icosahedral carborane derivatives bearing a variety of substituents on selected (generally antipodal) boron atoms. Reactions of the 9-substituted meta-carboranes, 9-R-1,7-C2B10H11 (R=OH, 4-MeC6H4, F, Cl, Br, I), with tetrabutylammonium fluoride hydrate (TBAFH) in refluxing THF gave nido-carborane salts containing a mixture of 1- and 6-R-7,9-C2B9H11− nido-anions. Regioselective deboronation occurred with the 9-halo-meta-carboranes, 9-X-1,7-C2B10H11 (X=F, Cl, Br, I), producing a 2:1 ratio mixture of nido 6-X-7,9-C2B9H11− and 1-X-7,9-C2B9H11−. Calculated Mulliken charges at B2 and B3 of some 9-substituted-meta carboranes show that these vary in line with observed deboronation rates and product ratios in their reactions with TBAFH. The ortho-carborane derivative 9-I-1,2-C2B10H11 and TBAFH gave the tetrabutylammonium salt of the nido anion 5(6)-I-7,8-C2B9H11−. The mercurated and thallated meta carboranes, 9-M-1,7-C2B9H11 (M=HgOCOCF3 and Tl(OCOCF3)2), with TBAFH underwent boron–metal bond cleavage to yield mainly the nido anion 7,9-C2B9H12−. Multinuclear (11B, 13C, 1H, 19F) NMR spectra of the carboranes have been recorded and assigned.

The laddering principle in lithium amide chemistry: the crystal and molecular structure of the pyrrolididolithium adduct [H2C(CH2)3NLi]3·MeN(CH2CH2NMe2)2

The title compound, {[H2[graphic omitted]NLi]3·PMDETA}n, (1)(PMDETA = pentamethyldiethylenetriamine), is shown to be the first example of an organonitrogen–lithium laddered structure, consisting in the solid (n= 2) of two attached (NLi)2 rings, or alternatively four (N–Li) rungs, with two terminal NLi units complexes by PMDETA, so preventing further association; cryoscopic and 7Li n.m.r. spectroscopic studies imply that extension of the ladder framework can occur in arene solutions of (1), and these results, together with those from ab initio m.o. calculations on model systems, suggest that similar compounds of type (RR′NLi·xdonor)n, but of various ladder lengths, should be preparable.

Azomethine derivatives. Part 20. Crystal and molecular structures of the lithioketimine [{Li(NCBut2)}6] and lithioguanidine [{Li[NC(NMe2)2]}6]; electron-deficient bridging of Li3 triangles by methyleneamino-nitrogen atoms

The lithioketimine Li(NCBut2)(1) and lithioguanidine Li[NC(NMe2)2](2) have remarkably similar hexameric structures [{Li(NCR2)}6](R = But or NMe2) in the crystal phase, based on slightly folded chair-shaped Li6 rings held together by triply-bridging methyleneamino-groups, NCR2, thus providing examples of electron-deficient bridging by the nitrogen atoms of organonitrogen ligands. The mean distance between adjacent metal atoms in the Li6 rings is 2.35(2)A in (1), and 2.445(2)A in (2), and the mean dihedral angles between Li6 chair seats and backs are 85 and 78° respectively. The nitrogen atoms of the bridging methyleneamino-groups are approximately equidistant from the three bridged metal atoms, the mean Li–N distance being 2.06(1)A in (1) and 2.00(1)A in (2). The NC distances of 1.30(1) and 1.244(3)A respectively lie within the range expected for carbon–nitrogen double bonds. Features of these structures are compared with those of related compounds, and some bonding implications are discussed.

A pentuply-bridging carbonyl group: crystal and molecular structure of a salt of the 1-oxo-2-phenyl-1,2-dicarbadodecaborate(12) anion, [LH]+[O(Ph)C2B10H10]− (L = 1,8-N,N,N',N'-tetramethylnaphthalenediamine)

Deprotonation of the C-hydroxy ortho-carborane 1,2-HO(Ph)C2B10H10 by 1,8-N,N,N′,N′-tetramethylnaphthalene-diamine gives a salt whose anion, [O(Ph)C2B10H10]–, effectively consists of a nido-shaped [PhCB10H10]– residue capped by a pentuply-bridging carbonyl group whose C–O distance of 1.245(3)A and position over the open carborane face, 2.001(3)A from the cage carbon atom, are readily rationalized by frontier orbital considerations.

X-ray crystallographic and solution studies of the pentamethyldiethylenetriamine and tetramethylethylenediamine adducts of lithium diphenylphosphide

X-ray crystallographic studies on the lithium diphenylphosphide adducts (Me2NCH2CH2)2NMe2 · LiPPh2 ( 1) and Me2NCH2CH2NMe2 · LiPPh2 (2) are reported. 1 is monomeric, with a terminal PPh2 unit containing a pyramidally coordinated phosphorus atom attached to the four-coordinate metal atom by a Li-P bond of length 2.567(6) A. 2 crystallizes as dimers, (Me2NCH2CH2NMe2 · LiPPh2)2, with bridging PPh2 units containing (distorted) tetrahedrally coordinated phosphorus atoms: their planar (LiP)2 rings are roughly square-shaped (mean PLiP angle 91°, mean LiP distance 2.61 A). Discussion of features of these structures is facilitated by ab initio MO calculations on the model systems LiPH2 and (LiPH2)2. Cryoscopic molecular mass measurements and high-field 7Li/31P NMR spectroscopic studies on solutions of 1 and 2 indicate that both solid-state structures are retained in arene solution, though some dissociation of2 into monomers is apparent.