Carbamoyl complexes

Nesmeyanov has provided interesting examples of apparent intramolecular nucleophilic attack by amine on carbonyl ligands (37). Angelici (38,39) has demonstrated that amine attack on cationic metal carbonyl complexes is a general reaction resulting in the formation of carbamoyl complexes ... 

These reactions serve to deplete the available nucleophile concentration. Furthermore, the formation of a relatively stable carbamoyl complex may serve to lower both the metal carbonyl and the nucleophile concentrations. 

The reaction of Mn(CO)jBr with [R NC(R )NR ]Li gibes the carbamoyl complexes (7), the reaction probably preceeding via nucleophilic attack at a... 

Reaction 21 for a tricarbonyl species could correspondingly be written instead of Reaction 17. The formation of carbamoyl complexes (M—CONRo) by the reaction of amines with metal carbonyls, especially cationic ones, has been reviewed by Angelici (24). Further studies are in progress. 

It was originally proposed that under the reaction conditions CO reduces the nitrobenzene 38a to nitrosobenzene 32. However, no free nitrosobenzene could be detected by trapping experiments. Instead, the carbamoyl complex 39 was isolated and crystallized (Figure 3.10) [135]. Although complex 39 showed decreased catalytic activity in the allylic amination as compared with [Cp Fe(CO)2]2... 

Carbacycles, via ring-closing diene metathesis large-sized, 11, 208 medium-sized, 11, 227 Carbamates, in semiconductor growth, 12, 27 Carbamoyl complexes, with mononuclear iron compounds,... 

C. Carbamoyl Complexes of Transition Metals with the Ligand... 

Completely different behavior toward liquid NH3 is shown by the three iron carbonyls Fe(CO)s, Fe3(CO)9, and Fes(CO),2 (98, 99) and the two cobalt carbonyls Co2(CO)8 and Co4(CO)i3 (100). Between -21 and 0°C, Fe(CO)5 and liquid NH3 give a homogeneous, pale-yellow solution from which Fe(CO)5 may be recovered on evaporating off the NH3. The solution contains the carbamoyl complex NHJfOC Fe—CONHJ which cannot be isolated and which is formed by nucleophilic attack of an NH3 molecule on a CO ligand, followed by proton release (101). At 20°C after 14 days of reaction, (NHJ FefCOlJ and CO(NH2)2 are obtained (99) ... 

As early as 1965, Angelici (108) was concerned with the reaction of Mn(CO)5Cl with primary and secondary aliphatic amines. He initially considered the product with MeNH2, namely, Mn(CO)5(NH2Me)(NHMe), to be a complex of heptacoordinated manganese. A subsequent X-ray structure analysis showed, however, that it is in fact a hexacoordinated carbamoyl complex, Mn(CO)4(NH2Me)CONHMe (109). In continuation of these studies, the reaction of cationic CO complexes of various tran-... 

The ionic species [Mn(CO)sNH3]CI, [Mn(CO)4(PPh3)NH3]Cl, and [Mn(CO)t(PPh3)2]Cl are formed from these carbamoyl complex series by reaction with HC1 in CgH6, according to the following type of reaction. jo... 

Thus, it may be assumed that, in analogy with the Hofmann acid amide degradation, the —CONH2 group of the carbamoyl complex is oxidized to NCO". 

Infrared data allow us to conclude that the carbamoyl complexes Co(CO)3(PPh3)CON Me2 and Co(CO)2(PPh3)(NH3)CONH2 have trigonal bipyramidal structures, with the —CONMe2 and PPh3 ligands of the tricarbonyl compound in axial positions (115). 

Table II shows a list of neutral carbamoyl complexes that we have synthesized from [T78-C5H5Fe(CO)2L]+ (L = CO, PPhs, PEt3), [(tj5-C5H4CHPh2)Fe(CO)2L]+ (C5H4—CHPh2 = diphenylmethylcyclopenta-dienyl L = CO, PPhs), and [(ij8-C7H8—CPh3)Fe(CO)3l+ (C7H8—CPh3 = triphenylmethylcycloheptadienyl) with liquid NHS (118).

On the basis of solid-state, IR-spectroscopic data for these carbamoyl complexes, we had earlier postulated a dimerization of two complex units via hydrogen bridges. This was later confirmed by X-ray structure analyses on other carbamoyl compounds (119,122). The dicarbonylcarbamoyl complexes always show cis-orientation of the CO ligands. 

The oxidation of these carbamoyl complexes with iodine is interesting, as they are converted to the respective isocyanato compounds in accordance with the Hofmann degradation of primary acid amides (118) ... 

The liberated HI reacts with part of the still-unoxidized carbamoyl complex to give the ionic starting material [T -CjHjFeCCOyi ... 

In the case of iron and ruthenium, we were successful in obtaining the first dinuclear carbamoyl complexes having (Pi = Ph2PCH2CH2PPh2) bridges and a —CONH2 ligand at both metal atoms (119). 

Understandably, these compounds having cis CO groups do not undergo a Hofmann acid amide degradation to give the respective hydrido complexes. The stability of these Group VIIIB carbamoyl complexes increases in the order Fe, Ru, Os. 

The last class of carbamoyl complexes with which we have been concerned has been that with NO+ ligands. For preparative and structural studies in this area, besides the cationic cyclopentadienylnitrosylcarbonyl complexes of Group VIIB 121), the nitrosylcarbonyl metal cations of Mo and W offer interesting starting materials 121). 

The nitrosyl ligand containing carbamoyl complexes of Mo and W are given in Table V (727). These compounds could also be converted into their carboalkoxo derivatives with MeOH. 

With the exception of [Re(CO)(CN)5]4, we have also been able to use new reactions in liquid NH3 to complete the series of possible cyanocar-bonylrhenates(H-I) (146). Despite numerous attempts by many research groups, preparation of Re(CO)sCN, isoelectronic with [W(CO)5CN], has remained elusive. In contrast, we were able to prepare the NHs-substi-tuted derivative/ac-Re(CO)3(NH3)2CN from Re(CO)sCl and KCN (molar ratio 1 1) in liquid NH3 at 120°C, and by removal of H20 and CO from the carbamoyl complex ris,-Re(CO)4(NH3)CONH2 in liquid NHS at the same temperature (112, 146). 

When carbon monoxide is bonded to a transition element, in a positively charged or even uncharged compound, the electrophilic capacity of carbon increases compared with the isolated molecule. Examples of nucleophilic attack are in equations (4) and (5). The reaction of methyl-lithium with W(CO)e giving the anioiuc acyl complex of equation (4a) is followed by alkylation to the carbene derivative of equation (4b). The formation of a carbamoyl complex with m-PtCl2(CO)2 is shown in equation (5). 

Formation of Carbon-Transition and Inner Transition Metal Bond 201 5.8.2.12. from Carbon Monoxide 5.8.2.12.4. Carbamoyl Complexes... 

Carbamoyl Complexes by Reaction of Metal Carbonyls with Amines. 

Rarely a carbamoyl complex can be isolated from an amine and a neutral (uncharged) metal carbonyl e.g., the reaction between Mn2(CO)jo and MeNH is ... 

Carbamoyl complexes are by the reaction of an amide ion with a cationic complex ... 

The reaction of an amine with a carboalkoxy-metal complex can be used to prepare a carbamoyl complex ... 

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