HMDB Hexamethyl benzene

HMBt + HMDB -> HMDBt -H HMB [HMDB = hexamethyl-Dewar benzene HMB = hexamethylbenzene]... 

Fused cyclobutene rings are easily opened. Hexam-ethyl(Dewar)benzene (HMDB) is thermolyzedto hexamethyl-benzene at 100-140 °C, but [RhCl(HMDB)]2 catalyzes the conversion at <70 °C. Since the catalyst itself is stable at 100 °C, it has been suggested that the catalyst is cleaved by excess substrate and that the rate-determining step is the elimination of hexamethylbenzene from [RhCl(HMDB)2]. 

Unsaturation is also important in the metal-catalysed disrotatory ring opening of XXXII ( hexamethyl-Dewar-benzene , HMDB) to hexamethylbenzene. This formally forbidden process is catalysed by monomeric HMDBRhCl (the reaction being of order 1/2 in [HMDBRhCl]2 and order 1 in substrate) Closely related is the conversion of XXXIII(a) to XXXIV, presumably by way of an unsaturated intermediate XXXIII ( ), since free CO or added alkene ligands inhibit the process . ... 

Unexpectedly, substituents on the phenyl group greatly effect the reaction pathway for mild thermolysis of hexamethyl Dewar benzene (HMDB) 70 in the presence of various azidobenzenes (Scheme 14). Thus, l-azido-2,4,6-trimethyl- and 1-azido-2,6-dimethylbenzene give 1,2-diazepines 71, whereas azidobenzene and 4-nitroazidobenzene give tetramethy lpyr-role 73. 

Hexamethyl Dewar Benzene (hexamethyl[2,2,0] hexa-2,5-diene, HMDB) can act as a bidentate ligand comparable to COD. The complex of HMDB with Cr(CO) (i.e. Cr(0)) is shown in D. IX where the two olefinic bonds occupy cis positions of a distorted octahedron 112>. 

Hexamethyl Dewar Benzene co-ordinates as a pz-allylic ligand with palladium (II). The structure of the complex [Pd(acac)dehydro-HMDB] is shown in D.XX mT With platinum, however, pz -o-bonding is preferred as in the dimeric planar [PtCl-dehydro HMDB]2, D.XXI 122>. 

---