Molybdenum, diene complex

In contrast to 73, the related tricarbonyl [2-(>/5-cyclopentadienyl)ethyI]-molybdenum (83) (107) forms fairly stable diene complexes with la-Ic in a stepwise reaction, first tj2- and, after prolongated irradiation, -coordinated [Eq. (44)]. Only to a minor extent is insertion of the dienes la and lb into the Mo—C [Pg.338]

Stereochemically, the [(f 5 1-C5H4C2H4)Mo(CO)(> 4-diene)] complexes 85a-85c are closely related to the 72-diene complexes 84a-84c, with the free C=C double bond in the former coordinated to the molybdenum instead of a CO ligand. Two rotamers can be expected, with C-l and C-4 of the dienes pointing toward the five-membered ring (o) or away from it (n). 

Very few i 4-diene halocarbonyl complexes of molybdenum(II) and tung-sten(ll) had been reported up to mid-1995. This section describes conjugated diene complexes, in Section VI,A, and nonconjugated diene complexes, in Section VI,B. 

The various heterocyclic ligands just described are easily cleaved from the respective molybdenum centers either by reaction with sulfur or through ligand exchange with l,2-bis(diphenylphosphino)ethane (Scheme 17).44a The Diels-Alder cycloaddition is successfully expanded to transient 1-phospha-1,3-diene complexes such as 25 and suitable dienophiles. As illustrated in Scheme 12, the isomeric 1,2-dihydrophosphetes (e.g., 26) are their masked stable precursors. Reaction of 26 with dimethyl acetylenedicarboxy-late or with benzaldehyde furnishes the Diels-Alder adducts of transient 25, compound 71, as a mixture of two isomers, and isomerically pure 72.44b (See Scheme 18.)... 

In contrast, molybdenum and iron diene complexes undergo the same type of reaction with chiral lithium imide enolates, with moderate to good induction at the p-position (eq 16). ... 

Reviews have appeared of the photophysics of molybdenum complexes, primary and secondary processes in organometallic chemistry, flash photolysis of Pe(CO)5 and Cr(CO)g, dinuclear manganese carbonyl compounds, the photochemistry of metal complexes isolated in low temperature matrices, cluster complexes, diene complexes, photoproduction of coordinativeiy unsaturated species containing rhodium or iridium, and redox chemiluminescence of organometallic compounds.Synthetic and metal organic photochemistry in industry has also been reviewed. 

External nucleophiles add to dienes complexed to metals other than palladium e.g., in the molybdenum complex VI either of the three re-ligands, the arene, the r-allyl group or the diene, can be attacked by the nucleophile ... 

The chemistry of dienes coordinated to the cationic CpMo(CO)j fragment has been exploited many times for complex molecule synthesis. Originally, Faller showed that the cationic molybdenum complex in Equation 11.44 undergoes nucleophilic attack by hydride, deuteride, methyl lithium, and enamines to produce the Ti -allyl complex. As expected, attack of the nucleophiles occurs at a terminal position and exclusively from the face opposite the metal. Trityl cation abstracts a hydride from this allyl product from the face opposite the metal to regenerate a diene complex. Pearson has used this sequence of nucleophilic attack and hydride abstraction to synthesize substituted cyclohexenes with control of stereochemistry as shown in Scheme 11.6. ... 

Mo(NAr)(CHCH=CMe2)(Me2Pyr)(OHMT) is relevant to the Z-selective homocoupling of 1,3-dienes by molybdenum and tungsten MAP complexes. The formation of the desired M=CHR complex can be complicated by the reformation of M=CHR or the metathesis of R CH=CH2 (when added in large excess) to give R CH=CHR and ethylene, which lead to the formation of methylidenes and unsubstituted metaUacyclobutane complexes. 

A number of molybdenum n3-allyl Ti -l,3-diene complexes have been synthesised3 and the X-ray structures of [CpMo(T]3,Ti4-Ci2Hi3)], [CpMo(Ti2,Ti -Ci4H 7)l tBF4l and [(Ti -C9H7)Mo(Ti2,ti4-Ci2Hi3)(Hmo,C-H)]+(CF3S03]- were reported. 

The complexes [PtR(OPh)(dmpe)] (R = Me, Et) have been prepared,566 and the X-ray structure of cis-[PtMe(OR)(PMe3)2].HOR [R = CH(CF3)2] in which the alcohol is H-bonded to the alkoxide ligand, has been determined.567 The transfer of methoxide from [PtMe(OMe)(dppe)] to a cationic molybdenum diene complex has been reported.568 The ammine complexes t/-a/w-[PtMe(NH3)L2]+ (L = phosphine) can be deprotonated to [LPtMe( i.-NH2)]2. which then react with L to form the... 

Acyclic diene molecules are capable of undergoing intramolecular and intermolec-ular reactions in the presence of certain transition metal catalysts molybdenum alkylidene and ruthenium carbene complexes, for example [50, 51]. The intramolecular reaction, called ring-closing olefin metathesis (RCM), affords cyclic compounds, while the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, provides oligomers and polymers. Alteration of the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

Simple 1,3-dienes also undergo a thermal monocyclopropanation reaction with methoxy(alkyl)- and methoxy(aryl)carbene complexes of molybdenum and chromium [27]. The most complete study was carried out by Harvey and Lund and they showed that this process occurs with high levels of both regio-and diastereoselectivity. The chemical yield is significantly higher with molybdenum complexes [27a] (Scheme 7). Tri- and tetrasubstituted 1,3-dienes and 3-methylenecyclohexene (diene locked in an s-trans conformation) fail to react [28]. The monocyclopropanation of electronically neutral 1,3-dienes with non-heteroatom-stabilised carbene complexes has also been described [29]. 

Eerrocene (1) was the first sandwich complex to be discovered, thereby opening a wide and competitive field of organometallic chemistry. The formation of ferrocene was found at almost the same time in two independent studies on July 11, 1951, Miller, Tebboth, and Tremaine reported that on the passage of N2 and cyclopenta-diene over a freshly prepared mixture of reduced Ee (90%), alumina (8%), potassium oxide (1%), and molybdenum oxide (1%) at 300°C, yellow crystals identified as Cp2Ee (Eig. 1) were obtained [1]. Due to the low yields obtained (3 g starting from 650 g ferric nitrate), doubts remain as to whether Ee(0) was the... 

Z,Z)-l,4-Dialkoxy-l,3-dienes can be readily prepared from propargyl ethers and molybdenum carbene complexes (equation 185)307. High stereoselectivity in this reaction may be due to the formation of stable vinyl hydride complex with the enol ether. 

The metal-catalysed olefin metathesis (equation 122) when applied to dienes results in ring-closure and expulsion of an olefin (equation 123). Thus the molybdenum carbene complex 241 promotes the decomposition of the 1,6-heptadiene derivative 242 to a mixture of the cyclopentene 243 and ethylene (equation 124)122. An analogous reaction of the alcohol 244 gives 245 (equation 125), and 4-benzyloxy-l,7-decadiene (246) affords the cyclohexene 247 and 1-butene (equation 126). These transformations, which occur in benzene at room temperature, proceed in excellent yields122. 

Although numerous advantages are associated with the use of supercritical carbon dioxide (scC02) as an ecologically benign and user friendly reaction medium, systematic applications to metal-catalyzed processes are still rare. A notable exception is a recent report on the use of scC02 for the formation of industrially relevant polymers by ROMP and the eyelization of various dienes or enynes via RCM [7]. Both Schrock s molybdenum alkylidene complex 24 and the ruthe-... 

The symmetrical dienyne 58a was converted to a fused bicyclo [4.3.0] ring in 95% yield [17] (Eq. 27). With substrate 58c containing an unsymmetrical diene tether, two different products, 59c and 59c, were obtained in a ratio of 1 to 1 (Eq. 28). The reaction course in the formation of the different bicyclic rings is shown in Scheme 8. This dienyne metathesis is also catalyzed by tungsten or molybdenum complex 62 or 63 (Fig. 1), and a dienyne bearing terminal alkyne 58b could be cyclized to give 59b in 97% yield. 

---