Mechanism of the Palladium-Catalyzed Metal−Carbon Bond Formation. Isolation of Oxidative Addition and Transmetalation Intermediates

Abstract

To investigate the reaction mechanism of the Pd-catalyzed metal-carbon bond formation, the model compounds [η 5 -1-Ph 2 P-2,4-Ph 2 C 5 H 2 ](CO) 3 MI (M ) Mo, 12; M ) W, 13) have been prepared and their reactions studied under coupling conditions. Treatment of 12 and 13 with stoichiometric amounts of zerovalent palladium yields the complexes [η 5 -1-Ph 2 P-2,4-Ph 2 C 5 H 2 ](CO) 3 MPd(PPh 3 )I (M ) Mo, 16; M ) W, 17) by oxidative addition of the M-I moieties on Pd 0 . Subsequent reaction of intermediates 16 and 17 with 4-nitro-1-[2-(tributylstannyl)ethynyl]benzene (Bu 3 SnCtC(C 6 H 4 )p-NO 2 , 18) leads to the formation of the transmetalation products [η 5 -1-Ph 2 P-2,4-Ph 2 C 5 H 2 ](CO) 3 MPd(PPh 3 )CtC(C 6 H 4 )p-NO 2 (M ) Mo, 19; W, 20), which have been isolated and characterized. Complexes 13 and 17 have been also characterized by X-ray analysis.

Heterobimetallic RePd complexes bridged by η1:η5-Ph2PC5H4 ligand. Synthesis, electronic and crystal structure of (CO)2(PR3)(η5-C5H4PPh2)Re–PdCl2, R = Me and OMe

“…Similar deformations have been previously reported for related angles in complexes having a four member bimetallic ring Cp-M-Pd-P (M = Mo, W). 14, 29 Despite the variations already mentioned, the Re-CO distances and OC-Re-CO interbond angles are comparable to those measured in other trans dicarbonyl cyclopentadienyl rhenium complexes, possessing a four legged piano stool type of structure. 30,31…”

Secondary Interactions in Phosphane‐Functionalized Group 4 Cycloheptatrienyl–Cyclopentadienyl Sandwich Complexes

“…[29] In view of the picture that has been developed for the bonding and oxidation state assignment in Cht-Cp Group 4 metal complexes, [4,5,30] the metal-metal interaction in 14 can be formally regarded as a dative Pd 0 !Zr + IV bond, in which the Pd center acts as a Lewis base towards the Lewis acidic Cht-Cp sandwich moiety. This interaction is expected to be weaker than the metal-metal bonds in common "early-late" heterodimetallic complexes, [31,32] Again, the M05-2X functional was employed, [22] which has also performed well for predicting the energetics of van der Waals metal dimers. [33] For both complexes, the optimized molecular structures feature a Pd···Zr interaction with Pd À Zr = 3.320 and 3.156 for 15 and 16, respectively ( Figure 5).…”

Catalyzed M–C coupling reactions in the synthesis of σ-(pyridylethynyl)dicarbonylcyclopentadienyliron complexes

“…Previously, the Lo Sterzo group clearly demonstrated a close analogy between the Pd-catalyzed carbon-carbon and metal- 57,59 The mechanism of the Pd/Cu-and Pd-catalyzed pyridylethynylation of cyclopentadienyliron dicarbonyl iodide should be apparently analogous to that of the carbon-carbon coupling reactions. Some additional clues to the mechanisms of the formation of the complexes 1-3, 5 may be provided by a consideration of the reactions between Cp(CO) 2 FeI and 2-ethynylpyridine.…”

“…[52][53][54][55] The role of palladium catalysts in promoting these transformations was also investigated. 52,[56][57][58][59] Although, the Lo Sterzo approach was shown to be a valuable route to alkynyl complexes, the need for preparation of tin reagents and removal of tin impurities limits the appeal of this method. To overcome these disadvantages, one can use an organometallic analogue of the Sonogashira protocol, 60,61 where transition metal halides react with terminal alkynes to form metal alkynyls via the Pd/Cu-or Pd-catalyzed dehydrohalogenation route, which provides milder reaction conditions and facilitates purication of products.…”