Reactions arene displacement

The allenylidene-mthenium complexes I also catalyze the enyne metathesis to alkenylcydoalkenes with a 1,3-diene stmcture. Initial studies showed the transformation of simple enynes with ether function [37] (Scheme 8.5). This reaction was significantly accelerated by initial catalyst photodiemical activation, which is now understood to favor the rearrangement of the allenylidene- into the active indenylidene-ruthenium moiety and arene displacement. 

Arene-displacement reactions, characteristics, 1, 97 Arene-ene substrates, in C-H bond alkylation, 10, 218 Arene-ferracarboranes, characteristics, 3, 225-226 I // -Arene liruliiim complexes, preparation, 7, 388 (Arene)metal(diborolyl) sandwiches, synthesis, 3, 12... 

More recently, two types of Ru complexes were obtained by the reaction of mesityl-substituted electron-rich olefins with [RuCl2(p-cymene)]2 [27]. Cleavage of the chlorine bridges occurs first to yield the expected (NHC)(p-cymene)Ru(II) complex 9. Under harsher reaction conditions (140 °C in p-xylene) further arene displacement takes place to yield the chelated ( 6-mesityl-NHC - Ru complex 10 (Scheme 6). The olefin 8 was easily obtained by deprotonation of the corresponding dihydroimidazolium salt. 

Facile arene displacement is favored by hard donor solvents (T), particularly oxygenated ones like acetone, THF, and water. Reaction with MeCN shows second-order kinetics with activation parameters consistent with a SN2 mechanism where the MeCN adds directly to the metal. This reaction is 104 times faster for Re than for the Mn analog, due to the larger size of Re, thus explaining why preparations employing hydrolytic work-up work well for Mn but not for Re. 

The macrocyclic calix[4]arene complex (Ti(Bu -calix[4]arene))2 was prepared from Ti(NMe2)4 and the neutral ligand. One of the four O atoms of each ligand bridges the two titanium centers.673 The related complex TiCl(But-calix[4]arene(0Me)(0)3) (61) was synthesized by a salt metathesis reaction. Subsequent displacement of the Cl by alkyl or aryl groups was readily accomplished.674... 

J0 The reaction of [Fe(t) -arene)] and Tl2[ V/o-7,8-C2B9Hii] results in arene displacement and formation of [l-(ij -arene)-c/oso-l,2,3-FeC2B9Hii] where the number of methyl substituents on the arene vary from 1 to 6 (B. Stfbr, M. Bakardjiev, J. Holub, A. Ruzicka, Z. Padelkovd, P. Stepnicka, Inorg. Chem., 2011, 50, 3097). Explain why product yields were lowest for the pentamethylbenzene and hexamethylbenzene complexes. Provide four unique trends (spectroscopic and electrochemical) that were correlated to increasing methyl substitution at the arene. 

Arene displacements (Equation 5.44) and arene exchange reactions (Equation 5.45) have been loiown since Strohmeier first studied arene exchange, " and Traylor has... 

Many similarities exist between metallabenzenes and conventional arenes. Among these similarities are structural features such as ring planarity and the absence of bond length alternation, spectroscopic features such as downfield chemical shifts for ring protons, and chemical reactions such as electrophilic aromatic substitution and arene displacement from (arene)Mo(CO)3. All of these features, taken together, strongly support the thesis that metallabenzenes represent a new class of aromatic compounds, one in which metal d orbitals participate fully with carbon p orbitals in the formation of ring 7r-bonds. 

Recently a suitable combination of a coordinating solvent (THF, acetone, dioxane) and an arene compound with a kinetically labile i-bonded ligand (anthracene, phenanthrene, naphthalene) that undergo the expected arene displacement reaction under milder conditions has been reported by Yag-upsky and Cai s (1975). 

A stepwise mechanism similar to that proposed for arene displacement reactions (see p. 178) cannot be eliminated. 

Bis ( -arene) metal complexes have been made for many transition metals by the AI/AICI3 reduction method and cationic species [M( j -Ar)2]"" " are also well established for n = 1, 2, and 3. Numerous arenas besides benzene have been used, the next most common being l,3,5-Mc3C6H3 (mesitylene) and CeMce. Reaction of arenas with metal carbonyls in high-boiling solvents or under the influence of ultraviolet light results in the displacement of 3CO and the formation of arena-metal carbonyls ... 

Novel ruthenium-amidinate complexes of the type (j -CgHsRlRufamidina-te)X (R = Me, OMe, F X = Cl, Br, OTf) and [Ru(amidinate)(MeCN)4][PF6] have been synthesized by photochemical displacement of the benzene ligand in (j -CgHglRufamidinatelX by substituted arenes or MeCN. The acetonitrile ligands of [Ru(amidinate)(MeCN)4][PF6] are easily replaceable by other cr-donor ligands (L) such as pyridines, phosphines, and isocyanides to afford the corresponding derivatives [Ru(amidinate)(MeCN) (L)4 ][PF6] n — 1, 2). These reactions are summarized in Scheme 142. ... 

A different synthetic access to a 1 -metallacyclopropene, which can be a versatile organometallic synthon, is displayed in Scheme 33. The mono-alkyne derivatives of W(IV)-calix[4]arene are easily accessible through the thermal displacement of cyclohexene from 32 using the appropriate acetylenes. The reaction led to complexes 34 and 172-174. The proposed 3-metallacyclopropene has been confirmed from the spectroscopic and the X-ray data. The H NMR data reveal a cone conformation of the calixarene with a four-fold symmetry, for which the... 

Loss of Coordinated Arene. We previously stated that the arene ligand in ruthenium(II)-arene complexes is relatively inert towards displacement under physiological conditions. While this is generally true, there are a few exceptions to this rule and this type of reactivity can be used to advantage. Weakly bound arenes, for instance, can be thermally displaced, a property convenient for the synthesis of ruthenium-arene complexes that are not readily available through more common synthetic routes. This way, the reaction of a precursor dimer, [RuCl2(etb)]2 (etb, ethylbenzoate) (68), with either 3-phenyl-1-propylamine or... 

From Chapter 7 it is apparent that the trichloromethyl anion is formed under basic conditions from chloroform, as a precursor of the carbene. The anion can also react with Jt-deficient alkenes (see Section 7.3) and participate in nucleophilic substitution reactions, e.g. 1,1-diacyloxy compounds are converted into 1,1,1-trichloroalkan-2-ols [58] (Scheme 6.35). Similarly, benzyl bromides are converted into (2-bromoethynyl)arenes via an initial nucleophilic displacement followed by elimination of hydrogen bromide [59] (Scheme 6.35). 

The mechanism by which a nucleophile displaces the diazonium group depends on the nucleophile. While some displacements involve phenyl cations, others involve radicals. Nucleophiles, e.g. CN , Cl and Br , replace the diazonium group if the appropriate cuprous salt is added to the solution containing the arene diazonium salt. The reaction of an arene diazonium salt with cuprous salt is known as a Sandmeyer reaction. 

---