Tricarbonyl[N,N′,N′′-tris(2,6-diisopropylphenyl)guanidine]molybdenum(0)

In the title compound, [Mo(C37H53N3)(CO)3], the Mo atom to ring-centroid distance in the η6-coordinated tricarbonylmolybdenum group is 1.958 (1) Å. The three C O groups are pseudo-octahedrally disposed with C—Mo—C angles ranging from 80.7 (1) to 87.4 (1)°. The two uncoordinated 2,6-diisopropylphenyl-substituted benzene rings form dihedral angles of 75.96 (8) and 78.01 (9)° with the mean plane of the guanidine group. The coordinated benzene ring is in a slight sofa conformation with the N-substituted C atom and the bonded N atom dispaced by 0.090 (3) and 0.458 (4) Å, respectively, from the mean plane of the remaining ring atoms. In the crystal, despite there being two N—H donor groups, no conventional hydrogen bonds are present. This may be because of the steric effects of the bulky diisopropylphenyl groups.

In the title compound, [Mo(C 37 H 53 N 3 )(CO) 3 ], the Mo atom to ring-centroid distance in the 6 -coordinated tricarbonylmolybdenum group is 1.958 (1) Å . The three C O groups are pseudo-octahedrally disposed with C-Mo-C angles ranging from 80.7 (1) to 87.4 (1) . The two uncoordinated 2,6diisopropylphenyl-substituted benzene rings form dihedral angles of 75.96 (8) and 78.01 (9) with the mean plane of the guanidine group. The coordinated benzene ring is in a slight sofa conformation with the N-substituted C atom and the bonded N atom dispaced by 0.090 (3) and 0.458 (4) Å , respectively, from the mean plane of the remaining ring atoms. In the crystal, despite there being two N-H donor groups, no conventional hydrogen bonds are present. This may be because of the steric effects of the bulky diisopropylphenyl groups.

Comment
The molecular stucture of the title compound, (I), is shown in Figure 1. The X-ray crystal structure of N,N',N"-tris(2,6diisopropylphenyl)guanidine (II) was reported by  with the three aryl groups in the same syn-anti conformation (Gopi et al., 2010) as found in compound (I). Table 1 presents the selected geometric data for compounds (I) and (II). Coles (2006) has comprehensively reviewed the application of neutral amidines and guanidines as coordination ligands. Recently, a cobalt(II) complex of the title ligand has been used as a catalyst in the synthesis of polysubstituted arenes via the regioselective cyclotrimerization of alkynes (Eichman et al., 2011). Also, deprotonated N,N',N"-aryl guandines have been reported to stabilize low-coordinate As(III) cations (Brazeau et al., 2011).
The title compound has an η 6 -coordinated tricarbonylmolybdenum group with a Mo to ring-centroid distance of 1.958 (1)Å. The three C≡O groups are pseudooctahedraly disposed with C-Mo-C angles ranging from 80.7 (1) to 87.4 (1)°.
The three 2,6-diisopropylphenyl rings have normals that are disposed at 79.78 (8)° (C3-C7), 75.96 (8)° (C14-C19) and 78.01 (9)° (C26-C31) to the guanidine plane defined by C1, N1-N3. The ring coordinated by Mo(CO) 3 is bent back from the core such that C2 is located 0.090 (3) and N1 0.458 (4)Å from the plane defined by C3-C7. In the crystal, despite there being two N-H donor groups, no conventional hydrogen bonds are present. This is possibly due to the steric effects of the bulky diisopropylphenyl groups. The orientation of the Mo(CO) 3 unit and its geometric parameters are found to be very similar in compound (I) and in closely comparable tricarbonylmolybdenum complexes of structurally similar amidines (Boeré, Klassen & Wolmershäuser, 1998. The observed outward bending of the coordinated aryl ring suggests that some steric effects operate between the amidine/guanidine groups and the Mo(CO) 3 units.

Experimental
The compound was prepared by a thermal reaction between the neural guanidine ligand and Mo(CO) 6 as described in . Full characterization by elemental analysis, NMR, mass spectrometry and infra-red spectroscopy are provided there.

Refinement
Hydrogen atoms attached to carbon were refined using a riding model with temperature factors of 1.2 (CH) or 1.5 (CH 3 ) × the equivalent isotropic values of the attached atoms. H2 and H3 attached to nitrogen were positionally refined using distance restraints of 0.88 Å and temperature factors 1.2 × the equivalent isotropic values of N2 and N3. Two reflections have unusually large deviations from the weighted errors of their intensities; no obvious cause could be determined for this effect. The isopropyl methyl groups are found to librate more than other carbon atoms but this effect is commonly observed in 2,6-diisopropylphenyl compounds. A rotational disorder model for isopropyl groups was judged to be unwarranted. Similarly, the carbonyl group oxygen atoms display considerable thermal motion, but this is also a well known behaviour, see Braga & Koetzle (1988 Fig. 1. The molecular structure of (I) shown with 30% probability ellipsoids. H atoms bonded to C atoms are not shown.