Daniel L. Ormsby

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.

Polyhedral azadicarbaborane chemistry. The ‘converse’ synthesis of a small family of 6,9-(NHR)-bridged-arachno-5,10-dicarbadecaboranes

Abstract Addition of PhCCH to hypho-type species [(R′H2N)B8H11NHR] proceeds readily with the displacement of R′NH2 to give corresponding N-bridged arachno ten-vertex species [6,9-μ-(NHR)-5-Ph-arachno-5,10-C2B8H10] (15–34%), for which DFT structural and GIAO 11B nuclear shielding calculations suggest the syn configurations that have the R and Ph groupings on the same side of the molecule.

Phosphacarborane chemistry. New cluster isomers in the eleven-vertex nido-phosphadicarbaborane series: synthesis of the nido phosphadicarbaboranes 7,8,11-PC2B8H11, [7,8,11-PC2B8H10]- and 7-Ph-7,8,10-PC2B8H10

Abstract The reaction between Na 2 [ nido -6,9-C 2 B 8 H 10 ] (glyme, RT, 24 h) and PCl 3 produced the neutral phoshadicarbaborane nido -7,8,11-PC 2 B 8 H 11 (35%), which can be quantitatively deprotonated by proton sponge to give the corresponding [7,8,11- nido -PC 2 B 8 H 10 ] − anion. A similar reaction using PhPCl 2 as the phosphorus source yielded the isomeric compound 7-Ph-7,8,10- nido -PC 2 B 8 H 10 (64%), as well as nido -7,8,11-PC 2 B 8 H 11 (14%) resulting from an accompanying dephenylation process.

The Parent Hexacarbaboranearachno-C6B6H12 and a Methylated Pentacarbaboranearachno-CH3C5B7H12: Domains of Incipient Hydrocarbon Behavior within Borane Clusters

Increasingly pronounced hydrocarbon character is exhibited by C6 H6 B12 , the first unsubstituted hexacarbaborane, and CH3 C5 B7 H12 , the first cluster pentacarbaborane. These compounds shed light on the structural dichotomy between open hydrocarbon skeletons and polyhedral borane frameworks for high-carbon carboranes.

Macropolyhedral boron-containing cluster chemistry: Models for intermediates en route to globular and discoidal megaloborane assemblies. Structures of [nido-B10H12(nido-B5H8)2] and [(CH2CH2C5H4N)-arachno-B10H10(NC5H4-closo-C2B10H10)] as determined by synchrotron X-ray diffraction analysis

Abstract A {B20H28} species, from the oligomerisation of B5H9, has a central nido {B10H12} core with two nido {B5H8} units bound to it at mutually adjacent positions. [(CH2CH2C5H4N)-arachno-B10H10(NC5H4-closo-C2B10H10)], a by-product from the reaction of [B10H12(NCMe)2] with ortho-ethynyl-pyridine, has mutually linked closo {C2B10} and arachno {B10} cluster units conjoined to a central aromatic pyridine unit; the arachno {B10} residue is also fused to an organyl double-ring structure involving a second pyridyl moiety. Both species model possible steps to globular megaloborane synthesis via the assembly of boron hydride units around a central cluster core, as well as having other interesting features. The small size of the crystals for both compounds necessitated the use of synchrotron X-radiation for sufficient diffracted-beam intensity for crystallographic analysis.

Macropolyhedral boron-containing cluster chemistry. A synthetic approach via the auto-fusion of [6,9-(SMe2)2-arachno-B10H12]

In an attempt to build up borane-based multicluster assemblies, thermolysis of [6,9-(SMe2)2-arachno-B10H12] 1 in inert hydrocarbon solution, followed by chromatographic separation, has resulted in the isolation not only of the previously established single-cluster product from this reaction, [5-(SMe2)-nido-B10H12] 2 (30%), but also the two two-cluster species [6,9-(SMe2)2-arachno-B10H11-1-(6-nido-B10H13)] 3 (20%) and [1,6-(nido-B10H13)2] 6 (ca. 0.5%) and the two three-cluster species [6,9-(SMe2)2-arachno-B10H10-1,5-(6-nido-B10H13)2] 4 (5%), characterized crystallographically, and [6,9-(SMe2)2-arachno-B10H10-1,3-(6-nido-B10H13)2] 5 (<1%), identified by NMR spectroscopy. An improved crystallographic investigation of [5-(SMe2)-nido-B10H12] 2 is also presented. The feasibility of the stability of species resulting from multiple adjacent substitution of nido-decaboranyl units on the [6,9-(SMe2)2-arachno-B10H12] skeleton is tested by DFT calculations. In an extension, to attempt the use of pre--linked two-cluster compounds as starting substrates, two-cluster [5-(SMe2)-4-(2-nido-B10H13)-nido-B10H11] 7 (0.6%) has been isolated from the reaction of SMe2 with [1,5-(nido-B10H13)2], other identified products being compound 1 (39%) and compound 3 (10.5%).

Monocarbaborane anion chemistry. The substantiation of the C-arylated [PhCB6H6]− seven-vertex closo cluster anion by single-crystal synchrotron X-ray diffraction analysis

Single-crystal synchrotron X-ray diffraction analysis of the [NEt4]+ salt of the [2-Ph-closo-2-CB6H6]− anion, obtained from [4-Ph-arachno-4-CB8H13] and NEt3 in refluxing toluene, substantiates the anion as the first structurally characterised seven-vertex monocarbaborane.

Bond rotamers and calculated 11B-NMR chemical shifts in boron-containing cluster chemistry. Some effects in the {nido-7,8,10-PC2B8} system

Abstract Rotamer changes about the exo -cluster C-phenyl bond in 7-Ph- nido -7,8,10-PC 2 B 8 H 10 have significant differential effects of up to ca . 6 ppm on the nuclear shieldings of adjacent boron atoms within the cluster. The phenomenon has some more general implications.

Unexpected formation of new fluoroboranes from the reaction of NMe4B3H8 with BF3 and MeCCH: exo-2-FB4H9 and trans-MeCHCHBF2

The new fluoroboranes exo-2-FB4H9 1 and trans-MeCH=CHBF2 2 have been obtained unexpectedly and in good yield from the reaction of tetramethylammonium octahydrotriborate (NMe4B3H8) with boron trifluoride and propyne (MeC identical to CH).

A new nido-5-vertex cluster, phosphacarba-nido-pentaborane, 2-tBu-1,2-PCB3H5.

The gas-phase reaction of the phosphaalkyne P identical to CtBu with tetraborane(10), B4H10, yields the nido five-vertex phosphacarbaborane cluster compound 2-tBu-1,2-PCB3H5 2 with an unusual 31P NMR peak shift of -500.5 ppm.