Stability terminal

It is interesting to note that the reactivity of the excited states of (25), (26), (27), and (28) in Table 8.4 increases in this order as stabilizing terminal substitution is increased. Zimmerman suggests that vinyl-vinyl bridging (the start of bond formation between 2 and 4) controls the reaction rate. 

Fig. 7. Formation and reactivity of base-stabilized terminal borylene complexes of osmium.

Roper, however, succeeded in converting the osmium boryl complex [Cl2BOsCl(CO)(PPh3)2] (E) into the terminal borylene complex [Os (=BNHC9H6N)Cl2(CO)(PPh3)2]147 (26) upon reaction with 8-aminoquino-line according to Fig. 7. Compound 26 is noteworthy as it represents the first example of a base stabilized terminal borylene complex of the type [LXM = B(L)-R] (IVa, Fig. 1). 

The X-ray crystallographic structure of the base stabilized terminal stannylene complex f-Bu2Sn(py)Cr(CO)5 is shown in Fig. 12 (95). The slightly longer Sn—Cr bond length in this complex, and the slight eleva-... 

The chemistry of these heterometallic compounds based on the M—O—motif covers main-group elements, transition metals, and lanthanides. The generation of the M—O—motif (21) requires the successful s)mtheses and stabilization of well-defined hydroxides. A considerable effort has been ongoing to stabilize terminal hydroxides of main-group and transition metals (22). Recently, a number of well-defined hydroxides of main-group and transition metals 1-11 (Chart 1) have been made (23-35) by careful hydrolysis of suitable precursors. Some of these hydroxides were used as building blocks to synthesize heterometallic complexes with M—O—backbones by reaction with catalyti-cally active transition metal complex precursors. 

Lithiated epoxides are more commonly trapped by electrophiles, generating elaborated oxiranes. In this arena, Hodgson and co-workers <04OL4187> have optimized the lithiation of non-stabilized terminal epoxides with iec-hutylhthium assisted by diamine ligands, such as dibutylbispidine (DBB, 99) or (-)-sparteine 100. The oxiranyl anions thus formed engage in smooth nucleophilic addition onto aldehydes to form epoxyalcohols e.g., 101) the same conditions can be used for the stannylation of epoxides e.g., 84 102). Similarly,... 

Figure 7.32 features a base stabilized terminal phosphinidene complex with a phosphorus resonance that is signihcantly upheld from those previously encountered. According to the x-ray crystal structure determination of this compound, the Fe—P bond order is one, and thus a single bond. It foUows that the phosphorus atom has the oxidation state +/ and the coordinahon geometry around phosphorus is tetrahedral with a stereoactive lone pair. 

Fig. 7.32 The base-stabilized terminal phosphinidene complex [TpPFe(CO) ]...

Figure 28 Example of a transition metal complex containing a hydrogen bond-stabilized terminal oxygen atom.

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