John F. Harrod

Polymerization of primary silanes to linear polysilanes catalyzed by titanocene derivatives

Abstract The dehydrogenative coupling of primary silanes to linear polysilanes is catalyzed by Cp2TiR2 (R = CH3 or C6H5CH2). The degree of polymerization of the polymers thus far obtained is ca. 10. Some physical and chemical characteristics of the polymers are described.

Homogeneous Catalytic Hydrosilylation of Pyridines

The color change from yellow to violet allows the formation of the intermediate [Cp2 Ti(SiHMePh)(pyridine)] to be monitored in the reaction of PhMeSiH2 with a pyridine in the presence of the precatalyst [Cp2 TiMe2 ] [Eq. (a)]; the hydride [Cp2 TiH] is postulated to be the key intermediate in the catalytic cycle. The regioselective hydrosilylation of pyridine and also substituted pyridines can be catalyzed by the titanocene [Cp2 TiMe2 ]. R=Me, CO2 Et.

Oligomerization of phenylgermanes by catalytic dehydrocoupling

Abstract Phenylgermane and diphenylgermane both show greater activity towards dehydrocoupling with a dimethyltitanocene catalyst than do their silane analogues. Phenylgermane polymerizes to a three-dimensional gel with dimethyltitanocene as catalyst and undergoes stepwise oligomerization with a vanadocene catalyst. Diphenylgermane is selectively dimerized to tetraphenyldigermane with a dimethyltitanocene catalyst. Reaction of diphenylgermane and dimethyltitanocene in equimolar ratio gives a purple product with properties similar to those exhibited by silyltitanocene(III) complexes reported earlier. This purple product is a powerful catalyst for the oligomerization of diphenylgermane and of tetraphenyldigermane to an oligomer consisting mainly of octaphenyltetragermane.

Catalysis of reactions of SiH by titanocene and its derivatives

Abstract This review describes the remarkable ability of titanocene derivatives to catalyze reactions of SiH compounds. These reactions involve addition of SiH to unsaturated molecules, dehydrocoupling of SiH with SiH and with a variety of other EH bonds, and redistribution of compounds containing the ROSiH bond system. The characterization of the many new titanocene complexes, which have been isolated as intermediates from these catalytic reactions, are also reviewed.

Titanocene‐Catalyzed Coupling of Amides in the Presence of Organosilanes To Form Vicinal Diamines

A sequence of reduction, deoxygenation, and coupling steps results in a remarkable reaction, which represents an important new method for the synthesis of 1,2-diamines. The vicinal diamines are formed by the facile coupling of aromatic amides in the presence of titanocene catalysts and PhMeSiH2 .

Characterization of poly(dihalophenylene oxides) in solution

Several different dihalophenylene oxide polymers prepared by thermal decomposition of halophenoxo copper complexes were studied in toluene using light scattering. For polymers of molecular weight around 5 × 104, those obtained from 4-bromo-2,6-dichlorophenoxide, 2-chloro-4,6-dibromophenoxide and 2,4,6-tribromophenoxide appear to be relatively linear with higher values of 〈S2〉12, whereas those obtained from 2,4,6-trichlorophenoxide and 2-bromo-4,6-dichlorophenoxide appear to have branched or condensed structures with lower values of 〈S2〉12. Values for the intrinsic viscosities and second virial coefficients were measured from ∼17 to 50°C for poly(dichlorophenylene oxides) synthesized from 2,4,6-trichlorophenoxide (Mw = 5.3 × 104) and from 4-bromo-2,6-dichlorophenoxide (Mw = 2.49 × 105). These quantities both pass through a maximum as the temperature increases.

A systematic analysis of the structure-reactivity trends for some ‘cation-like’ early transition metal catalysts for dehydropolymerization of silanes

Abstract The use of ‘cation-like’ metallocene combination catalysts (Cp′ 2 MCl 2 2BuLiB(C 6 F 5 ) 3 ; Cp′ = η 5 -cyclopentadienyl, or substituted η 5 -cyclopentadienyl; M = Ti, Zr, Hf, U) for dehydropolymerization of silanes significantly improves the polymer molecular weight. For example, under the same conditions a Cp(C 5 Me 5 )ZrCl 2 2BuLi catalyst gives M n = 1890, while a Cp(C 5 Me 5 )ZrCl 2 2BuLiB(C 6 F 5 ) 3 gives M n = 7270. The influence of various factors (steric and electronic effects of the cyclopentadienyl ligands, the nature of the metal, temperature, solvent, concentration and structure of silane) on the build-up of polysilane chains are systematically analyzed.

The influence of the catalyst preparation protocol and silane structure on the rate and enantioselectivity of ansa-titanocene catalysed hydrosilation of prochiral ketones

Abstract The hydrosilation of prochiral ketones using catalysts prepared by alkylation of [1,2-bis(tetrahydroindenyl)ethane]titanium IV (1,1′-binaphth-2,2′-diolate) with MeLi and n-BuLi, and (EtO) 3 SiH, Me(EtO) 2 SiH, [MeSi(H)O] 4 , Me 3 SiO[MeSi(H)O] n SiMe 3 and MeSiH 3 as the hydrosilane is described. The rates obtained with the MeLi based catalyst are one to two orders of magnitude faster than previously observed with MeLi based catalysts in the presence of MePhSiH 2 and Ph 2 SiH 2 and about the same as those observed with n-BuLi based catalysts. Me(EtO) 2 SiH, [MeSi(H)O] 4 and Me 3 SiO[MeSi(H)O] n SiMe 3 all undergo rapid redistribution in the presence of the catalyst to give MeSiH 3 , the actual hydrosilating agent in all three cases. Likewise, (EtO) 3 SiH redistributes to SiH 4 . The ee s for the hydrosilation product of acetophenone are consistently much higher (∼99%) for the n-BuLi based catalyst than for the MeLi based catalyst (∼40–50%). The hydride complex [(BTHIE)TiH] 2 gives essentially the same enantioselectivity as the MeLi based catalyst. The ee s for a test set of dialkylketones are relatively insensitive to either the catalyst or the hydrosilane. Some possible mechansims that are consistent with the experimental results are discussed.

Reactions of silanes with allylic alcohols catalyzed by titanocene derivatives: an approach to catalytic cross dehydrocoupling/co-intramolecular hydrosilation

A preliminary study of the dimethyltitanocene, 7, and rac-[ethylene-1,2-bis(η5-4,5,6,7-tetrahydroindenyl)]TiMe2, 8, catalyzed reactions of silanes with allylic and homoallylic alcohols is described. In the presence of catalysts 7 or 8, tertiary silanes bearing at least one phenyl group react with 2-methyl-but-1-ene-4-ol, 2a, to produce the 4-siloxy-2-methylbut-1-ene, 3a. Secondary silanes react with either 2a, or 2-methylpropen-3-ol, 2b, to give different product distributions depending on the catalyst type, concentration, and the substituents on the silicon atom. With high catalyst concentration and diphenylsilane, a redistribution reaction substantially converts the initially produced allyloxydiphenylsilane to bis(allyloxy)diphenylsilane. Low catalyst concentrations give primarily the intramolecular hydrosilation product. Under the same reaction conditions, phenylmethylsilane gives more intramolecular hydrosilation product than diphenylsilane does. Phenylsilane reacts with 2b, to give a polymeric product, 6b (R  Ph, R′  H), via intermolecular hydrosilation. Under the same conditions phenylsilane reacts with 2a to give primarily the hydrogenation product tris(3-methylbutoxy)phenylsilane, 5a (R  Ph, R′  -OCH2Ch2CH(CH3)2), together with traces of oligosilane and intermolecular hydrosilation product 6a. Some possible reaction pathways, including the observed side reactions, are discussed.

Homogen katalysierte Hydrosilylierung von Pyridinen

Anhand des Farbwechsels von Gelb zu Violett last sich die Bildung der Zwischenstufe [Cp2Ti(SiHMePh)(Pyridin)] bei der Reaktion von PhMeSiH2 mit einem Pyridin in Gegenwart der Katalysatorvorstufe [Cp2TiMe2] verfolgen [Gl. (a)]; als Schlusselintermediat im Katalysecyclus wird das Hydrid [Cp2TiH] diskutiert. Mit dem Titanocen [Cp2TiMe2] kann die regioselektive Hydrosilylierung von Pyridinen katalysiert werden, die auch substituiert sein konnen. R=Me, COOEt.