Current mechanisms for the transition metal-catalyzed ring-opening polymerization (ROP) of [1]-ferrocenophanes and related strained species such as cyclic carbosilanes invoke a homogeneous mechanism. In this paper we describe experiments which indicate that the Pt(0)-catalyzed ROP of silicon-bridged [1]-ferrocenophanes proceeds mainly by a heterogeneous mechanism with colloidal platinum as the catalyst. Mechanistic studies were initiated to elucidate the fate of the ferrocenylsilane component of the precatalyst, fcPt(1,5-cod)SiMe 2 (4) (fc ) Fe(η 5 -C 5 H 4 ) 2 ), a proposed intermediate in the catalytic cycle for fcSiMe 2 (1a) with Pt(1,5-cod) 2 as the initiator. The ring-opened addition product Et 3 SifcSiMe 2 H (6) was isolated in high yield from the Pt(0)-catalyzed ROP of 1a in the presence of 35-fold excess of Et 3 SiH. Species 6 and Et 3 SiH were subsequently employed as capping agents in the Pt(0)-catalyzed ROP of fcSiMePh (1b) to generate model oligomers, Et 3 SifcSiMe 2 (fcSiMePh) n H (10, n ≈ 20) and Et 3 Si(fcSiMePh) n H (8, n ≈ 7), respectively. Copolymerization of a mixture of 1a and 1b using Pt(0) catalyst afforded a random copolymer (fcSiMe 2 -rfcSiMePh) n (9). Comparative end-group analysis of 8, 9, and 10 was performed with the oligoferrocenylsilane synthesized via the ROP of 1b in the presence of Et 3 SiH initiated by the precatalyst 4. Significantly, this revealed that the ferrocenyldimethylsilane component of 4 is not incorporated into the resultant polymer backbone which possessed the structure Et 3 Si(fcSiMePh) n H (8). Similarly, the ROP of 1a in the presence of Et 3 SiH initiated by the precatalyst fcPt(1,5-cod)Sn( t Bu) 2 (11) gave end-capped oligomers Et 3 Si(fcSiMe 2 ) n H (5), devoid of Sn( t Bu) 2 groups. The observations that the ferrocenylsilane and ferrocenylstannane components of 4 and 11 are not incorporated into the polyferrocene products and that, in addition, mercury was found to significantly retard ROP, indicates that the previously proposed homogeneous ROP mechanism is incorrect and that colloidal platinum is the main catalyst. A new heterogeneous mechanism for the platinum-mediated ROP of siliconbridged [1]ferrocenophanes is proposed which is likely to have important implications for the metal-catalyzed ROP mechanisms for related species such as silacyclobutanes.

271ChemInform Abstract Although the p-tolylcarbyne-W complex (I) does not itself react with alkynes, its protonation product, the title carbene, readily incorporates 1,2-diphenylacetylene (II) or 1,2-dimethylacetylene (IX) to give the vinylcarbene complex (III) and the η4-naphthol omplex (XI), respectively. The vinylcarbene complex (III) readily undergoes CO/I-substitution to yield the neutral vinylcarbene complex (V) (space group I2/a, Z = 8). With (BH4)-, (III) is converted into the allyl complex (VI). Treating (III) with the nitrone (VII) leads to the etallafuran complex (VIII) ( P21/n, Z=4) which possesses a planar metallafuran ring with bond distances in the ring implying delocalized bonding. The naphthol ligand from (XI) can be released by air oxidation. The naphthol ligand undergoes deprotonation to form the eutral allyl complex (XII). Reaction of the carbyne complex (XIII) with HBF4 in the presence of 1,2-dimethylacetylene (IX) under CO (X) leads to the formation of the diene complex (XIV) by benzannulation reaction from the carbyne, alkyne, and one CO ligand. The elevance of these various reactions to the general mechanism of naphthol formation from metal carbenes and alkynes is discussed.

The importance of scorpionate ligands in modern coordination chemistry continues to increase, because of their outstanding versatility, tunability and user-friendliness. Herein, we provide a short overview of recent developments in the classes of scorpionate ligands, derived from pyrazoles, triazoles, imidazoles, oxazolines, thioimidazoles and other similar systems, followed by an in-depth discussion of a new type of ro- Classes of Scorpionate LigandsScorpionate ligands [1] are facially coordinating tridentate chelates, which have evolved into one of the most useful and [a]

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The reaction of 4-(dibromoboryl)styrene with 2pyridylmagnesium chloride resulted in the formation of 4-styryltris(2-pyridyl)borate free acid (StTypb), a new polymerizable nonpyrazolyl "scorpionate" ligand. StTypb did not undergo selfinitiated polymerization under ambient conditions and proved to slowly polymerize through standard radical polymerization at 90 °C. Nitroxide-mediated polymerization (NMP) of StTypb at 135 °C proceeded with good control, resulting in a polymer of M n = 27400 and PDI = 1.21. The TEMPO-terminated homopolymer successfully initiated the polymerization of styrene, generating an amphiphilic block copolymer with DP n of 1200 and 78 for the PS and the StTypb block, respectively. A similar block copolymer with DP n of 29 and 20 for the PS and the StTypb block respectively was obtained in a reverse polymerization procedure from a PS macroinitiator. The self-assembly of these block copolymers was examined in selective solvents and preliminary metal complexation studies were performed.