Thomas D. McGrath

Dirhodium (II) carboxylate complexes as building blocks. cis-Chelating dicarboxylic acids designed to bridge the dinuclear core

The syntheses and crystal structures of a series of dicarboxylic acids of general structure HO2CCR2OArOCR2CO2H (LH2) designed to span a pair of cis sites on the dirhodium(II) tetracarboxylate framework are described. Monochelate complexes LRh2(OAc)2 and bischelate complexes L2Rh2 were prepared by heating the diacids with Rh2(OAc)4 in N,N-dimethylaniline. Chelates were formed under kinetic control and the best yields were obtained from diacids with methyl groups on the ether side arms and bulky substituents on the aromatic ring next to the ether links. Effective molarities for chelation were measured under thermodynamic control by 1H NMR in tetrachloroethane. The stability of chelates and the conformational properties of diacids were investigated by molecular mechanics and quantum chemical techniques.

Dirhodium(II) carboxylate complexes as building blocks. Synthesis of dimeric species as connectors for macrocycles

Abstract Two complexes of the form (AcO)2Rh2LRh2(OAc)2 in which two Rh24+ units are covalently linked have been prepared by reaction of Rh2(OAc)4 with bischelating tetracarboxylate ligand L =( − O 2 CC ( Me ) 2 O )) 2 PhPh ( OC ( CH 3 ) 2 CO 2 − ) 2 in N,N-dimethylaniline. A crystal structure of the major (kinetic) product showed, unexpectedly, that it contained two 14 membered chelate rings, with the isomeric minor (thermodynamic) product having two 12 membered chelate rings.

Dinuclear complexes as connectors for carboxylates. Self-assembly of a molecular box

A dinuclear complex derived from dirhodium(II) tetraacetate has been used as a corner unit for the synthesis of metallomacrocyles, including a square box with aromatic side walls.

Formation of Intramolecular Rings in Ferramonocarbollide Complexes

Addition of PPh 2Cl and Tl[PF 6] to CH 2Cl 2 solutions of [N(PPh 3) 2][6,6,6-(CO) 3- closo-6,1-FeCB 8H 9] ( 1) affords the isomeric B-substituted species [6,6,6-(CO) 3- n-(PHPh 2)- closo-6,1-FeCB 8H 8] [ n = 7 ( 2a) or 10 ( 2b)]. Deprotonation (NaH) of the phosphine ligand in 2a, with subsequent addition of [IrCl(CO)(PPh 3) 2] and Tl[PF 6], yields the neutral, zwitterionic complex [6,6,6-(CO) 3-4,7-mu-{Ir(H)(CO)(PPh 3) 2PPh 2}- closo-6,1-FeCB 8H 7] ( 3), which contains a B-P-Ir- B ring. Alternatively, deprotonation using NEt 3, followed by addition of HC[triple bond]CCH 2Br, affords [6,6,6-(CO) 3-7-(PPh 2CCMe)- closo-6,1-FeCB 8H 8] ( 4). Addition of [Co 2(CO) 8] to CH 2Cl 2 solutions of the latter gives [6,6,6-(CO) 3-7-(PPh 2-{(mu-eta (2):eta (2)-CCMe)Co 2(CO) 6})- closo-6,1-FeCB 8H 8] ( 5), which contains a {C 2Co 2} tetrahedron. In the absence of added substrates, deprotonation of the PHPh 2 group in compounds 2, followed by reaction of the resulting anions with CH 2Cl 2 solvent, affords [6,6,6-(CO) 3- n-(PPh 2CH 2Cl)- closo-6,1-FeCB 8H 8] [ n = 7 ( 6a) or 10 ( 6b)] plus [6,6-(CO) 2-6,7-mu-{PPh 2CH 2PPh 2}- closo-6,1-FeCB 8H 8] ( 7, formed from 2a), of which the latter species possesses an intramolecular B-P-C-P- Fe ring. Addition of Me 3NO to CH 2Cl 2 solutions of 2a causes loss of an Fe-bound CO ligand and formation of [6,6-(CO) 2-6,7-mu-{NMe 2CH 2PPh 2}- closo-6,1-FeCB 8H 8] ( 8), which incorporates a B-P-C-N- Fe ring. A similar reaction in the presence of ligands L yields [6,6-(CO) 2-6-L-7-(PPh 2CH 2Cl)- closo-6,1-FeCB 8H 8] [L = PEt 3 ( 9) or CNBu (t) ( 10)], in addition to 8.

Synthesis, structure and reactivity of η4(5e)-butadienyl substituted molybdenum complexes

Reaction of lithium halides with the cationic complexes [Mo(NCMe)(η2-alkyne)2L](L =η-C5H5 or η5-C9H7) afforded the halogeno-bis(alkyne) substituted molybdenum complexes [MoX(η2-alkyne)2L](X = Cl, Br or I). A single-crystal X-ray diffraction study of the complex [MoI(η2-MeC2Me)2(η-C5H5)] showed that the two alkyne ligands lie approximately parallel to the Mo–I vector and the plane of the η-C5H5 ligand. Reaction of [MoX(η2-RC2R)2(η-C5H5)] with HBF4·Et2O afforded excellent yields of the aqua complexes [Mo{C(R)-η3[C(R)C(R)CHR]}X(OH2)(η-C5H5)][BF4](X = Cl, R = Me 9; X = Cl, R = Et 10; X = Br, R = Et 11 and X = I, R = Et 12); a single-crystal X-ray diffraction study of the cation 11 confirmed the presence of co-ordinated H2O and of a η4(5e)-butadienyl fragment in an anti-supine conformation, the water occupying a co-ordination position trans to the MoC bond. The H2O ligand in these cations can be displaced by acetonitrile allowing the synthesis of the complexes [Mo{C(R)-η3-[C(R)C(R)CHR]}X(NCMe)(η-C5H5)][BF4](X = Br, R = Me 13; X = Br, R = Et 14 and X = I, R = Et 15). A single-crystal structure determination of 14 confirmed the overall geometry of the complex and showed that the co-ordinated MeCN also occupies a position trans to the MoC bond. Treatment of the aqua complexes with LiX resulted in the formation of the neutral dihalogeno complexes [Mo{C(R)-η3-[C(R)C(R)CHR]}X2(η-C5H5)](X = Cl, R = Me 16; X = Cl, R = Et 17; X = Br, R = Et 18; X = I, R = Et 19 and X = Br, R = Me 20). The structure of 18 was confirmed by X-ray crystallography, and it was also found that the mixed dihalogeno complex [Mo{C(Et)-η3-[C(Et)C(Et)CHEt]}ClI(η-C5H5)]21, is formed in high yield on reaction of the acetonitrile-substituted complex 15 with LiCl. Reaction of trimethyl phosphite with the aqua- or acetonitrile-substituted cations resulted in the stereoselective formation of the complexes [Mo{C(R)-η3-[C(R)C(R)CHR]}X{P(OMe)3}(η-C5H5)][BF4](X = Br, R = Me 23; X = Cl, R = Me 24 and X = Br, R = Et 25). A single-crystal X-ray study of 23 confirmed the presence of a cisoid anti-supine η4(5e)-butadienyl ligand and also showed that the P(OMe)3 ligand occupies a position cis to the MoC bond. In contrast, treatment of the aqua complexes with the poorer π-acceptor PMe3 afforded isomeric mixtures of substitution products. However, reaction of complex 14 with PMe3 afforded a complex which was structurally identified by X-ray crystallography as [Mo{C(Et)-η3-[C(Et)C(Et)CHEt]}Br(PMe3)(η-C5H5)][BF4]26a where the phosphine ligand is cis to the MoC bond. The base, Li[N(SiMe3)2], reacted with 24 to give the X-ray crystallographically identified, air-sensitive, η4-vinylallene complex [MoCl{η4-CH(Me)C(Me)C(Me)CCH2}{P(OMe)3}(η-C5H5)]28, which upon treatment with HBF4·Et2O reformed the η4(5e)-butadienyl complex 24. When 23 was reacted with AlHBui2 the 1,3-diene complex [MoBr{η4-CH(Me)C(Me)C(Me)CH(Me)}{P(OMe)3}(η-C5H5)]29 was formed. Reaction of this air-sensitive molecule with [Ph3C][BF4] regenerated 23. The structures and mechanisms of formation of these various new types of complexes are discussed.

Macropolyhedral boron-containing cluster chemistry. Characterisation ofrigid 77-atom[Pt(B18H20)2]2-dianion isomers and an unusual metallaborane homophilic interaction

Reaction of [Pt(cod)Cl 2 ] (cod = cycloocta-1,5-diene) with [NEt 4 ] 2 [anti-B 18 H 20 ] or with [syn-B 18 H 22 ] and tmnda (tmnda = N,N,N′ ,N′-tetramethylnaphthalene-1,8-diamine) resulted in the generation of [Pt(anti-B 18 H 20 ) 2 ] 2 - or [Pt(syn-B 18 H 20 ) 2 ] 2 - dianions, for which intramolecular steric crowding imposes rigid slab structures, and which have unusual intimately packed anion-layer structures in their salts in the solid state.

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.

Enhanced slip distortions in 1-phenyl-2-methyldicarbaplatinaboranes. Conformational destabilisation in the isomerisation of 1-phenyldicarbaplatinaboranes

The compounds TI2[7-Ph-8-Me-7,8-nido-C2B9H9], [C5H10NH2][7-Ph-8-Me-7,8-nido-C2B9H10], 1-Ph-2-Me-3,3-L2-3,1,2-PtC2B9H9[L = PMe2Ph, PEt3, PPh3 or P(C6H4Me-p)3] have been prepared and characterised. The platinum complexes were obtained from the reactions between TI2[7-Ph-8-Me-7,8-nido-C2B9H9] and the appropriate [PtCl2(PR3)2] species. Crystallographic studies upon the compounds where L = PEt3 and two crystalline modifications of that where L = PPh3 afforded evidence of a substantial influence of intramolecular crowding upon the observed structures, so that the lateral slippage (Δ) of the metal fragment is significantly enhanced: Δ= 0.74 and 0.94 and 0.91 A respectively. These compounds do not isomerise under conditions which produce rearrangement in the corresponding (less-congested) derivatives of 1-phenylcarbaborane, consistent with the proposed conformational destabilisation in the latter system.