Multiple Bonds to Heteroatoms

For M=0 in an octahedral complex, there are strong interactions between two of the M orbitals and the O lone pairs (Fig. 11.4). When the two d orbitals are empty (cf to (f), the interaction is bonding, and 

Many metal oxos have electron configurations from cf to cf. The oxo wall is often invoked to explain the lack of isolable octahedral oxo complexes, particularly noticeable for the later transition metals. On this idea, M=0 groups are only stabilized by six-coordinate metal centers with an oxidation state of no less than 4+ and a d electron count no higher than (f or This is ascribed to destabilizing electron-electron 

Similar ideas hold for M =NR+ and M=N, where M =NR+ is linear at nitrogen, as expected for an M=N triple bond. The d (ri -QH4(/-Pr)Me)-Os =NAr+ and (T -C5Me5)Ir+=NAr+ avoid the azo wall by being linear. A rare bent M=NR double-bonded structure is found in 11.30, where the M=NR bond length of 1.789 A can be compared with the adjacent M=NR+ at 1.754 A. The reason for the unusual structure is that since =NR is an X2 and =NR is an LX2 ligand, if both imides were linear the Mo would have 20e. 

The complexes are often formed by oxidation, hydrolysis, or aminolysis (Eq. 11.43-Eq. 11.45). 

The M=0 band at 900-1100 cm in the IR spectrum is characteristic of the terminal 0x0 group M=NR+ appears at 1000-1200 cm and M=N at 1020-1100 cm The assignment can be confirmed by or substitution. An exception is Cp2M=0 (M = Mo,W), with y(M-O) frequencies below 880 cm electron counting shows that these must be M=0, not M=0, however, as is indeed consistent with the long 

FIGURE 11.7 ir-Bonding in metal oxo complexes. After the r bonds have been considered, a species has a two-above-three orbital pattern characteristic of 

Synthesis The complexes are often formed by oxidation, hydrolysis, or aminolysis (Eqs. 11.68-11.72). Equation 11.71 shows an unusual and very interesting route that forms multiple bonds to O and to C at the same time.  

The most oxophilic elements are even able to extract O from organic compounds, which prevents use of oxygenated solvents in many of these systems (Eq. 11.72). The nitride ligand has a lone pair that can sometimes be alkylated in a synthesis of an imido complex (Eq. 11.73)  

With more electrons on the metal, the bond order drops and electron-electron repulsions between M(J r) electrons and heteroatom lone pairs de.stabilize dre 

FIGURE 11.4 n Bonding in metal 0x0 complexes. Afta die a iionds have been con-sidoed, a species has a two above ihtec orbital pau characteristic of an 

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New aspects in the chemistry of multiple bonds to heteroatoms, considered in particular for 2-silanaphthalene and silabenzene stabilized with 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl substituent at the Si atom 99PAC405. 

II. Ruthenium and Osmium Complexes Containing Multiple Bonds to Heteroatoms... 

If the CH balance given by the CH multiplicities differs from the number of H atoms in the molecular formula, then the additional H atoms are bonded to heteroatoms. The C NMR spectra in Fig. 2.5 show, for example, for isopinocampheol (2), Cio// 0, a quaternary C atom (C), four CH units (C4//4), two CH2 units C2H4) and three CH3 groups (C3//5). In the C//balance, Cvfln, one H is missing when compared with the molecular formula, Cio// 0 to conclude, the compound contains one OH group. 

Cycloaddition of nitrile oxides to multiple bonds containing heteroatoms 93UK1164. 

At present, various options for defining breakable bonds are available on input. There is a choice of the kind of bond — multiple bonds, bonds to heteroatoms,... 

Besides carbon — carbon multiple bonds, carbon —heteroatom double bonds (C = 0 C = NR) are also capable of undergoing metal-catalyzed [3 4- 2] cycloadditions. However, the simplest class of substrates, i.e. ketones and imines, respectively, could so far only be employed when 2-(trimethylsilylmethyl)prop-2-enyl acetate (1) was used as a TMM synthon. These reactions, which additionally require the presence of cocatalysts such as tin or indium compounds when ketones are used as substrates, lead to the selective formation of 3-methylenetetrahydrofurans and 3-methylenepyrrolidines (3, X = O, N), respectively. ... 

This index was proposed to measure the molecule functionality, here intended as the presence of heteroatoms and multiple bonds. To avoid molecular size dependence, this functionality index is normalized by the number of atoms A ... 

An example of the hyper-Wiener-type index is the Lu index proposed to describe multiple bond and heteroatom-containing molecules [ Lu, Guo et al, 2006a, 2006b, 2006c], It is calculated from the bond ler h-weighted distance matrix D(r ) and defined as... 

This index was proposed as the first and simplest measure of graph cormectivity. Defined in the same way as the total adjacency index, but using different vertex degrees to take into account multiple bonds and heteroatoms, three other simple molecular descriptors were defined [Pogliani, 1992a] ... 

Functional groups are of two main types those that have a single bond to a heteroatom and those that have a multiple bond to a heteroatom. Alcohols, halides, ethers, and amines are examples of the first type, while aldehydes, ketones, and carboxylic acids are examples of the second type. 

Hydrocyanation is the addition of HCN across carbon-carbon or carbon-heteroatom multiple bonds to form products containing a new C-C bond. The majority of examples from organometallic chemistry involve the addition of HCN across carbon-carbon multiple bonds, as shown in Equations 16.2 and 16.3. Lewis acids and peptides have been used to catalyze the enantioselective addition of HCN to aldehydes and imines to form cyanohydrins and precursors to amino acids.The addition of HCN to unactivated olefins requires a catalyst because HCN is not sufficiently acidic to add directly to an olefin, and the C-H bond is strong enough to make additions by radical pathways challenging. However, a large number of soluble transition metal compounds catalyze the addition of HCN to alkenes and alkynes. 

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