Diazadienes as control ligands in homogeneous catalysis XVIII. Palladacyclopentadienes and platinacyclopentadienes and the co-cyclotrimerization of various alkynes

Dibenzometallacyclopentadienes, boroles and selected transition metal and main group heterocyclopentadienes: Synthesis, catalytic and optical properties

“…Recently, research has been concerned with the synthesis and characterization of metallacyclic intermediates, which can be isolated with the use of appropriate metal centers and ligands around the metal and studied as independent species [57]. Metallacyclic compounds of this type are known for a wide range of transition metals, including Ti [58,59], Zr [60], Hf [61,62], Pt [63], Pd [64], Ir [50,65], Ru [66], W [67,68], Fe [69], Au [70], Rh [71] and Co [53,72]. There are a vast number of such complexes, and their more complex derivatives, and these will not be reviewed here.…”

Synthesis, stability and reactivity of palladium(0) olefin complexes bearing labile or hemi-labile ancillary ligands and electron-poor olefins

“…Bulky ligands stabilize the Pd(0) alkyne complexes [56] which otherwise might add a further alkyne molecule to give palladium(II) cyclopentadienyl derivatives [57][58][59][60] according to a mechanism that was recently proposed and will be discussed later [44,61,62].…”

Rhodium-Catalyzed Chemo- and Regioselective Intermolecular Cross-Cyclotrimerization of Nonactivated Terminal and Internal Alkynes

“…A successful solution to minimize the chemo- and regioselectivity problems includes temporary connections of two or three different monoynes with disposable tether groups, such as boron and silyl groups. A practical solution to control both chemo- and regioselectivity in the completely intermolecular cross-cyclotrimerization of alkynes without the use of tether groups is the use of two or three different alkynes possessing different electronic properties. − For example, our research group reported the highly chemo- and regioselective cross-cyclotrimerization of nonactivated terminal alkynes and electron-deficient internal alkynes (dialkyl acetylene­dicarboxylates) to produce 3,6-disubstituted phthalates, catalyzed by a cationic rhodium­(I)/H 8 -BINAP complex at room temperature (Scheme , top). , This method has been successfully applied to the synthesis of paracyclophanes including cyclo­paraphenylenes . However, the chemo- and regioselective cross-cyclotrimerization without employing an electronically biased combination of alkynes has not been reported to date.…”