The Group IV -Methylene Congeners

Comparative Structural Data of ER2-Bridged Metalcarbonvl Derivatives (E = C, Si, Ge, Sn) 

ONE STEP BEYOND THE METHYLENE BRIDGE l (co,co )-ALKANEDIYL COMPLEXES 

Oligo- and polymethylene-bridged complexes can be prepared by reaction of metal carbonyl anions with w.w -dihaloalkanes. This method proved to be a simple entry to the iron series /j,-(CH2)j.][(t75-C5H5) Fe(CO)2]2 (x s 3) (283), but yielded quite different products in the case of Na[(T 5-C5H5)Mo(CO)3] (283) and Na[Mn(CO)s] (284). An alternative two-step synthesis of the iron compounds involves the preparation of the mononuclear w-haloalkyls LXM—(CH2)X—X, and a subsequent 

125 are not known, but the five-membered cycle very likely is not planar, although it could be if we compare it with the structure of the trinuclear ruthenium compound 126, the Ru2C3 core of which is strictly coplanar (289). This analogy, however, is admittedly overly simplistic since 126 

Structure of the four-membered dimetallacycle [ i-bis(trifluoromethyl)acetyl-ene]bis[carbonyl(r)5-cyclopentadienyl)rhodium](/ /i—Rh) (126a) (244), a typical example of a strictly planar M2C2 framework. Bond lengths in picometers. 

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