Udo Dörfler

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.

B-frame-supported bimetallics. Isoelectronic arachno-structured [(PMe2Ph)4Pd2B8H10] and closo-structured [(PMe3)4(CO)2Ir2B8H8]

Abstract Reaction of [IrCl(CO)(PMe 3 ) 2 ] with [NEt 4 ][ nido -B 9 H 12 ] gives the ten-vertex eight-boron cluster species [(PMe 3 ) 4 (CO) 2 Ir 2 B 8 H 8 ]. This formally has a closo cluster electron count compatible with its closo structure. By contrast, ten-vertex eight-boron [(PMe 2 Ph) 4 Pd 2 B 8 H 10 ], isolated from [4-(NH 2 Ph)- arachno -B 9 H 13 ] and [PdCl 2 (PMe 2 Ph) 2 ], has a closo electron count but an arachno structure. The origins of this apparent anomaly are briefly addressed and enunciated.

A rearrangement of the 10-boron nido / arachno decaboranyl cluster

Abstract Upon reaction with SMe2, [2,4-Cl2-nido-B10H12] gives [6,9-(SMe2)2-1,7-Cl2-arachno-B10H10] and [1,2,4-Cl3-nido-B10H11] gives [6,9-(SMe2)2-1,3,7-Cl3-arachno-B10H9] 1 , demonstrating a previously unsuspected fundamental rearrangement for the 10-boron arachno/nido cluster type.

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%).

POLYHEDRAL NONABORANE CHEMISTRY : AN UNSUSPECTED NEW ISOMERIC TYPE IN THE NINE-VERTEX ARACHNO-B9H13L SYSTEM

Abstract NMR spectroscopy reveals that the preparation of conventionally-structured 4-(ligand)- arachno -B 9 H 13 species 1 by ligand exchange on 4-(SMe 2 )- arachno -B 9 H 13 1a is often accompanied by the formation of their hitherto unsuspected and unreported 5-(ligand)- arachno -B 9 H 13 isomers 2 , which can be isolated by chromatography. 5-(4′-PhC 5 H 4 N)- arachno -B 9 H 13 2c is characterised by a single-crystal X-ray diffraction analysis that also reveals an interesting stacking of the organic aromatic residues in the solid state.

Polyhedral azaborane chemistry. The establishment of members of the hypho-type family [(RH2N)B8H11NHR], where groups R are now other than ethyl

The reaction of [B 9 H 13 (SMe 2 )] with primary amines NH 2 R to give eight-boron cluster species [(RH 2 N)B 8 H 11 NHR] is not limited to the case where R = ethyl. We find that the n-butyl, isopropyl and tert-butyl analogues are also readily formed. The structural type is illustrated by a single-crystal X-ray diffraction analysis on the isopropyl member of the family. The reaction proceeds stepwise, via an initial ligand exchange on [B 9 H 13 (SMe 2 )] to give [B 9 H 13 (NH 2 R)], as confirmed by treatment of [B 9 H 13 (SMe 2 )] with NH 2 Bu t to give [B 9 H 13 (NH 2 Bu t )] followed by treatment with Pr i H 2 N to give the mixed species [(Pr i H 2 N)B 8 H 11 NHBu t ], also confirmed by single-crystal X-ray work, and showing that the amine on the starting arachno-{B 9 H 13 } residue is the one that finishes in the more intimately bound bridging position.

Polyhedral azaborane chemistry. Nitrogen-vertex incorporation in metallaazaborane formation from 4-(NHEt2)B9H13. Two isomers of [(η5-C5Me5)RhB9H12(NEt2)]

The reaction of 4-(NHEt2)-arachno-B9H13 with [{RhCl2(η5-C5Me5)}2] and NaH afforded orange-yellow [6-(η5-C5Me5)-nido-6-RhB9H12-µ-8,9-(NEt2)] 1 and yellow [5-(η5-C5Me5)-nido-5-RhB9H12-µ-9,10-(NEt2)] 2. These compounds were characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy and are compared to their non-bridged congeners [6-(η5-C5Me5)-nido-6-RhB9H13] 3 and [5-(η5-C5Me5)-nido-5-RhB9H13] 4. It is concluded that the bridging µ-{NEt2} groups exhibit bonding to the borane cage that is intermediate between bonding schemes that involve one two-electron three-centre bond and two two-electron two-centre bonds.

2,4-Cl2-6,9-exo,endo-(PMe2Ph)2-arachno-B10H10

The title compound, 2,4-dichloro-6-exo-9-endo-bis(dimethylphenylphosphino)-arachno-decaborane(10) [(PMe2Ph)2B10H10Cl2 or C16H32B10Cl2P2], has a typical arachno ten-vertex cluster geometry, with one of the phosphine ligands bound exo-polyhedrally and the other in an uncommon endo configuration.

exo,endo and exo,exo isomers of 6,9-(PMe2Ph)2-arachno-B10H12 and its halogenated derivatives. Molecular structures of exo,endo- and exo,exo-6,9-(PMe2Ph)2-arachno-B10H12 and exo-6,endo-9-(PMe2Ph)2-2-Br-arachno-B10H11

Reaction of PMe2Ph with nido-B10H14 at ca. 200 K gave exo,exo and exo,endo isomers of 6,9-(PMe2Ph)2-arachno-B10H12 which were separated chromatographically. Both forms were confirmed crystallographically. The compounds 2-Br-nido-B10H13 and 2,4-Cl2-nido-B10H12 gave exclusively exo,endo forms at ca. 200 K with the 2-Br product consisting of equal amounts of 6-endo-9-exo and 6-exo-9-endo-(PMe2Ph)2 isomers, demonstrating no directional control by the 2-Br substituent. The relative configurations of the two brominated isomers were confirmed by a crystallographic study of the 6-exo-9-endo species. Both the monobrominated exo,endo isomers gave the exo,exo counterpart on heating, but the 2,4-Cl2 species is more robust, with apparent decomposition on extended heating, and no evidence for the formation of exo,exo-6,9-(PMe2Ph)2-2,4-Cl2B10H10.