Ruthenocene analogues

The condensation of respective l,r-bis(chlorocarbonyl)-metallocenes (1) and (2) [9, 10] with p-tert-butylcalix[4]arene [11] (3) in the presence of triethylamine gave, after column chromatography (alumina/CH2Cl2), the ferrocene calix[4]arene (4) (64% yield, orange crystals) and the ruthenocene analogue (5) (47% yield, pale yellow crystals) (Scheme 1). The structures of both new air-stable metallocene calix[4]arenes were verified by elemental analysis and mass spectrometry. The experimental details for their synthesis and characterisation will be reported elsewhere. 

Organometallic compounds are defined as compounds which contain at least one metal to carbon bond, other than metal carbides. Resolution of organometallic compounds by gas chromatography can be illustrated by citing the remarkable separation of ferrocene and its analogues, ruthenocene and osmocene. 

In a manner similar to that in Question 6-176, predict whether ruthenocene and osmocene (the ferrocene analogues of ruthenium and osmium) would be stable compoimds Explain. 

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