Oxime-derived chloro-bridged palladacycles 12 and 13 are efficient complexes for the Suzuki-Miyaura reactions of aryl-, allyl-, and benzyl halides with arylboronic acids. The isolated catalysts are thermally stable, not sensitive to air or moisture, and easily accessible from inexpensive starting materials. The reaction can be performed under aerobic conditions with aryl bromides and chlorides, displaying turnover numbers (TON) of up to 5 x 10(5) and turnover frequencies (TOF) of up to 198 000 h(-1) for aryl bromides. Aryl chlorides undergo the Suzuki reaction with arylboronic acids with TON of up to 4700 and TOF up to 4700 h(-1). Even inexpensive and readily available benzyl and allyl chlorides undergo the coupling reaction with good turnover numbers. Complexes of 12 catalyze the syntheses of symmetrical biaryls in good yields via reductive coupling of iodoarenes in the presence of Hünig's base.

The reaction mechanism for the Pd-catalyzed Cu-free Sonogashira reaction is analyzed by means of density functional theory (DFT) calculations on a model system. The most common routes proposed in the literature for this reaction, namely, the carbopalladation and deprotonation, are considered. In agreement with experiment, calculations clearly demonstrate that the carbopalladation route can be discarded. For the case of the deprotonation route, however, the reaction pathway may take place via several alternatives; calculations suggest that all of them are feasible. Moreover, an additional pathway where the halide is initially replaced by the base in the coordination sphere of the catalyst is found to be also competitive. The effects of the alkyne’s substituents on the reaction are also analyzed by a combined computational and experimental work. Theoretical results suggest that these effects are rather small, and they are confirmed by experiments.

Scheme 42. Reactions of Fluoropropargylic Organozinc Derivatives Reported by Hammond and Co-Workers Scheme 43. In-mediated Synthesis of Fluorinated Allenes Reported by Hammond and Co-Workers Scheme 44. Alkylation of Nonterminal Propargylic Fluorides Chart 4. Propargylic Fluorides as Insecticides, Arthropodicides, Herbicides, and Fungicides

Oxime-derived chloro-bridged palladacycle 8a, derived from 4,4'-dichlorobenzophenone, is an efficient pre-catalyst for the copper-and amine-free Sonogashira coupling between terminal acetylenes and aryl iodides and aryl and vinyl bromides achieving turnover numbers (TON) of up to 72000. Catalyst 8a has also been shown as a effective promoter for the sila-Sonogashira coupling between 1-(trimethylsilyl)alkynes and aryl iodides and bromides in the presence of CuI or Bu 4 NBr as co-catalysts. This complex also catalyzes efficiently the homocoupling reaction (Glaser-type coupling) between 1-alkynes in NMP at room temperature with TONs of up to 1000. All the reactions can be performed under air and employing reagent-grade chemicals under very low loading conditions, which demonstrates the versatility and high activity of oxime-derived palladacycles.

Phosphane-free oxime-derived palladacycle 2 is an efficient precatalyst for the copper-free acylation of terminal alkynes with different carboxylic acid chlorides in toluene in the presence of 3 equiv of TEA as base, giving the corresponding ynones in good yields. The coupling reaction can normally be performed under air or under inert atmosphere when very low catalyst loadings (10(-3) mol % Pd) (turnover numbers (TONs) up to 23,000, turnover frequencies (TOFs) up to 958 h(-1)) or sensitive carboxylic acid chlorides are used. In addition, Pd(OAc)(2) has been shown as an efficient catalyst for the ligandless process, although usually working under higher loading conditions. This new protocol allows one to perform the synthesis of ynones at 110 degrees C, at room temperature, or under microwave irradiation conditions.