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Bis(pentamethylcyclopentadienyl)dihydridozirconium(IV), (eta/sup 5/-C/sub 5/Me/sup 5/)/sub 2/ZrH/sub 2/ (2) is prepared by the reaction of H/sub 2/ with ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrN/sub 2/)/sub 2/N/sub 2/ (1). 2 forms unstable adducts with PF/sub 3/ and CO at -80/sup 0/C. The carbonyl adduct (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH/sub 2/(CO) yields ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH)/sub 2/(OCH == CHO) and/or (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH(OCH/sub 3/), depending on reaction conditions. Carbonylation of (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CH/sub 3/)/sub 2/, obtained from (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrCl/sub 2/ and methyllithium, yields successively (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CH/sub 3/)(CH/sub 3/CO) and (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(O(CH/sub 3/)C == C(CH/sub 3/)O). The zirconacyclopentane ecomplex (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CH/sub 2/(CH/sub 2/)/sub 2/CH/sub 2/) (10) is prepared from 1 and ethylene. Carbonylation of 10 affords (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)-(OC == OH(CH/sub 2/)/sub 2/CH/sub 2/). Treatment of 2 with isobutylene yields (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)(Ch/sub 2/CHMe/sub 2/) (13), which undergoes a reaction with CO to form (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)(OCH == CHCHMe/sub 2/) (15). The results of /sup 13/C and deuterium labeling studies indicate that the conversion of 13 to 15 is mediated by (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)(Me/sub 2/CHCH/sub 2/CO). The observed patterns formore » these reactions of alkyl and hydride derivatives of zirconium with CO are attributed to carbenoid character of the carbonyl carbon resulting from an unusual ''side-on'' coordination of acyl and formyl groups.« less

Principles of M-C and M-H bonding interactions are examined experimentally by high-resolution valence photoelectron spectroscopy. Gas-phase He I and He II photoelectron spectra are reported for the following series of d{sup 0} and d{sup 2} bent metallocenes: Cp{sub 2}MH{sub 3} (M = Nb, Ta), Cp{sub 2}M(CO)L (M = Nb, Ta; L = H and M = Nb; L = CH{sub 3}), and Cp{sub 2}M(C{sub 2}H{sub 4})L (M = Nb, Ta; L = H and M = Ta; L = C{sub 2}H{sub 5}) (Cp = {eta}{sup 5}-C{sub 5}H{sub 5}). The ligand replacements represented by this series of complexes allow stepwise comparison and assignment of each individual low-energy valence ionization band. The He I/He II spectral comparisons show that the lowest ionization energy band of the carbonyl complexes is higher in metal character than the corresponding ionization of the ethylene complexes. This trend indicates extensive electron delocalization in the metal-ethylene bonding that corresponds more accurately to a metallacyclopropane description with relatively strong metal-carbon bonds. The photoelectron data for the early transition metal hydride and alkyl species show that the metal-hydrogen bonds are slightly more stable than the metal-carbon bonds. Correlation of the ionization information for these substituted early metallocenes reveals that themore » stabilization of the metallacyclopropane-hydride structures, M(C{sub 2}H{sub 4})H, relative to the olefin-inserted metal-alkyl structure, M(C{sub 2}H{sub 5}), is partly due to stabilization of the metal electron density by back-bonding to the olefin as indicated by earlier theoretical studies.« less

The photocatalyzed isomerization of 1-pentene to trans- and cis-2-pentene by Ru(CO)4PPh3 and Ru3(CO)9(PPh3)3 is reported along with data for Ru3(CO)12, Fe3(CO)12, and Fe(CO)5. The primary photoprocess in Ru(CO)4PPh3 is dissociative loss of CO giving a coordinatively unsaturated species having the same empirical formula Ru3(CO)9(PPh3)3; the trinuclear species undergoes Ru-Ru bond rupture and ultimate declusterification subsequent to photo-excitation giving a quantitative yield of Ru(CO)4PPh3 under CO or Ru(CO)3(PPh3)2 in the presence of PPh3. The crucial result is that the cluster yields a different catalytically active species compared to Ru(CO)4PPh3, since the initial ratio of trans- and cis-2-pentene is different for the two photocatalysts. The photocatalysis and primary photoprocesses suggest that the isomerization from the Ru3(CO)9(PPh3)3 results from an active form of the cluster. By way of contrast, Fe(CO)5 and Fe3(CO)12 yields the same initial ratio of photocatalytic products, implicating a common, mononuclear catalytic species. Since the clusters are good visible absorbers compared to the mononuclear species, photoactivation of cluster catalysis can be effected with low energy visible light.

Reduction of CO in moderate yields was observed when ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CO))/sub 2/N/sub 2/ was treated with HCl. Further studies revealed that mononuclear carbonyl and hydride complexes of bis(pentamethylcyclopentadienyl)zirconium were capable of promoting the stoichiometric H/sub 2/ reduction of CO to methoxide under very mild conditions.