Diaryls bridged

The HI and H2 substitutents were ethers, methylene, ethylene, and diaryl bridges or hydride substituents. Thus these positions were either involved in an intemnit link or hydride substituted in the present model. Greater proportions of the thermally labile ether linkages were in the MWL while the laaft lignin contained greater proportions of more stable methylene, ethylene, diaryl and diaryl linkages. The PI and P2 substituents could be an ether, such as that listed... 

Another method for reductive dimerization has been developed in hy-drosilylation. NiCl2-SEt2 is an effective catalyst in silylative dimerization of aromatic aldehydes with a hydrosilane (Scheme 12) [40]. A catalytic thiolate-bridged diruthenium complex [Cp RuCl(/ 2-SPrI)2RuCp ][OTf] also induces the conversion to 1,2-diaryl-1,2-disiloxyethane [41]. A dinuclear (siloxyben-zyl)ruthenium complex is considered to be formed, and the homolytic Ru - C bond fission leads to the siloxybenzyl radicals, which couple to the coupling product 14. 

A pinacol-type silylative dimerization of various aromatic aldehydes promoted by a cationic thiolate-bridged diruthenium complex has been reported by Flidai and co-workers (Equation (28)).344 l,2-Diaryl-l,2-disiloxyethanes 153 were isolated as the major products along with the corresponding arylmethyl silyl ethers as minor products. 

Diaryl- and triaryl-methane dyes also fall into this class [(124) is known as Michler s Hydrol Blue] and a number of the heterocyclic derivatives of these dyes are well known. Introduction of a sulfur bridge into Michler s Hydrol Blue (124) results in the dye Thiopyronine (125) which absorbs at 565 nm. The analogous dye with an oxygen bridge, Pyronine, absorbs at 545 nm and that with an —NH— bridge, Acridine Orange, absorbs at 490 nm (B-76MI11201). 

Analogous cyano complexes can be prepared. Treating the bis chelate complex [Pt(dppm)2]2+ with 2 equivalents of NaCN leads to stabilization of the r 1-dppm complex (151) which can be used to prepare heterobimetallic bridging complexes with added M (M= Ag+/I, HgCl2, Rh2Cl2(CO)4) (equation 433).1461 Similar complexes can be formed with dialkyl and diaryl substituents on platinum in place of cyanide.1462... 

It is also relevant to record that several iron-carbonyl complexes with bridging, and in one case terminal, aryltellurol ligands have been prepared by reaction of Fe(CO)5, Fe(CO)12 or [ji-CpFe(CO)2]2 with diaryl ditellurides and which, together with complexes containing other transition metal carbonyls, e.g, ruthenium, osmium and manganese, provide a substantial number of interesting compounds.2... 

Dibenzophospholes A and dithienophospholes B and C (Fig. 4.7) do not display the typical electronic properties and reactivity patterns of phospholes, since the dienic system is engaged in the delocalized benzene or thiophene sextet [7, 10a, 51]. In fact, these building blocks have to be regarded as nonflexible diaryl-phosphines or as P-bridged diphenyl or dithienyl moieties. 

A different sequential DreM pathway involving O-carbamate ring switch-vinylogous tolyl amide cydization, 170 —> 171 —> 172 (Scheme 44), a formal bridging of a 2,2 -methyl diaryl dicarbanion with a carbonyl dication equivalent (173) has been affirmed in a model study (174 —> 175, Scheme 45) [73] and applied in natural product total synthesis [73, 74]. 

Scheme 46. Heteroatom-bridged diaryl DreM routes to heterocycles.

Diaryl ditellurium compounds react with iron carbonyls in benzene solution to form dinuclear, arenetellurolato-bridged iron complexes1 7... 

The dissymmetic (C2 symmetry) dihydrodinaphthothiepin 43 and related bridged diaryl derivatives are of interest because the stereoisomers can be separated (atropisomers) and have potential applications as chiral reagents. An X-ray crystal study of compound 43 shows that it has a cisoid arrangement around the biaryl bond with an interplane angle of 66.1 <1995T787, CHEC-III(13.03.3.1)102>. 

---