Synthesis and Molecular Structure of cis -Tetracarbonyl[ N -(diphenylphosphino-k P )-naphthalen-1-yl-P , P -diphenylphosphinous amide-k P ]chromium(0)

The reaction of N , N -bis(diphenylphosphanyl)naphthylamine C 10 H 7 -1-N(PPh 2 ) 2 with (C 5 H 10 NH) 2 Cr(CO) 4 (1: 1 molar ratio) in dichloromethane afforded cis -[Cr(CO) 4 { C 10 H 7 -1-N(PPh 2 ) 2 } ] (1) . This complex was crystallized in the monoclinic space group P 2 1 /n. The structure was solved by direct methods and refined by full-matrix least squares techniques to an 𝑅 factor of 0.0313 for 6488 observed reflections. The Cr-metal is coordinated by four terminal CO molecules and a P , P 󸀠 -bidentate N , N -bis(diphenylphosphanyl)naphthylamine ligand in a distorted octahedral array. The N-atom adopts a planar geometry with the two P-atoms and C-atom attached to it. The four-membered metallacycle ring P 2 CrN is nearly


Chemistry.
All experiments were carried out under purified dry nitrogen using standard Schlenk and vacuum line techniques. Solvents were dried and freshly distilled under nitrogen [10]. The chemicals Cr(CO) 6 were used as purchased. C 10 H 7 -1-N(PPh 2 ) 2 [1] and (C 5 H 10 NH) 2 Cr(CO) 4 [11] were prepared according to the literature methods. Infrared spectra were recorded on a Shimadzu FTIR-8400S spectrometer between 4000 and 400 cm −1 using KBr disks. The NMR spectra were recorded at 25 ∘ C on a Bruker-Avance-DRX-400 MHz NMR spectrometer operating at 400.17 ( 1 H) and 100.63 ( 13 C) using tetramethylsilane as external standard.
Melting point was carried out on a Gallenkamp apparatus with open capillaries.

Data Collection and Structure
Determination. Crystallographic data are given in Table 1. Single-crystal X-ray diffraction data were collected using an Oxford Diffraction Supernova dual-source diffractometer equipped with 13.954 (5) No. of params 415 a 135 mm Atlas CCD area detector. Crystals were selected under Paratone-N oil, mounted on micromount loops, and quench-cooled using an Oxford Cryosystems open flow N 2 cooling device [12]. Data were collected at 150 K using mirror monochromated Cu K radiation ( = 1.5418Å) and processed using the CrysAlisPro package, including unit cell parameter refinement and interframe scaling (which was carried out using SCALE3 ABSPACK within CrysAlisPro) [13]. Equivalent reflections were merged and diffraction patterns were processed with the CrysAlisPro. The structure was subsequently solved using direct methods and refined on F2 using the SHELXL 97-2 package [14][15][16]. All nonhydrogen atoms were refined with anisotropic displacement parameters. All H-atoms bonded to carbon atoms were placed in geometrically optimized positions and refined with an isotropic displacement parameter relative to the attached atoms. Crystallographic data (excluding structure factors) for the structure in this paper has been deposited with the

Results and Discussion
3.1. Synthesis. Complex 1 was previously prepared by the reaction of Cr(CO) 6 with C 10 H 7 -1-N(PPh 2 ) 2 in refluxing toluene for 36 hours [1]. Here, an alternative synthetic methodology was devised using (C 5 H 10 NH) 2 Cr(CO) 4 instead of Cr(CO) 6 in refluxing CH 2 Cl 2 to avoid prolonged refluxing time and further purification of the desired product. This methodology gave 1 in high yield and without the need for further purification. The NMR data are in agreement with those reported previously in the literature [1].

Molecular
Structure. Yellow colored crystals of 1 were obtained as described in the Experimental Section. 1 crystallizes in the monoclinic space group P2 1 /n. Selected interatomic distances and angles are collected in Table 2. The molecular structure is depicted in Figure 1. The crystal structure of 1 shows a distorted octahedral environment around the Cr-metal surrounded by four terminal CO ligands and two phosphorus centers (Figure 1).
The ability of the N,N-bis(diphenylphosphanyl)naphthylamine ligand to act as bidentate P,P -chelating ligand to the Cr-metal results in the formation of a four-membered metallacycle, that is, P-Cr-P-N, that is approximately planar with a torsion angle P-Cr-P-N of −9.66(5) ∘ , with a smaller P-Cr-P bite angle [68.74(3) ∘ ] and larger P-N-P bond angle [100.70(7) ∘ ] ( Table 2). The nitrogen atom is displaced out of the plane (Cr1, P1, P2) by 0.2873 (14)Á.
To the best of our knowledge, there are other three structurally characterized monocyclic four-membered ring complexes of bidentate P,P -chelating bis(phosphino)amine  [19]. A comparison of the structural data of the P-Cr-P and P-N-P bond angles in 1 ( Table 2)  The P-N-P [100.70(7) ∘ ] bond angle is significantly smaller than those in the free diphosphinoamine ligands [19,20] due to the formation of a strained four-membered chelate ring.
The C-napthyl skeleton in 1 is almost planar and virtually perpendicular to the P-Cr-P-N plan. A planar environment would be expected for the three-coordinate nitrogen atoms in 1 and the sum of bond angles is indeed close to 360 ∘ ( Table 2). The P-Cr-C trans angles of 1 [166.57 (7)  1.692Å] and significantly shorter than the sum of Pauling covalent radii (1.77Å) as expected due to P-N -bonding. Consistent with this, the nitrogen atom is planar as evidenced by the sum of angles about nitrogen being 359.91(9) ∘ for 1. Also, the P-N bond distances in 1 are slightly shorter than those in the free diphosphinoamine ligands [19,20] which clearly indicate an enhancement of -bonding in the P-N unit.
The Cr-C bond distances are 1.859(2)-1.883(2)Å for 1. The two Cr-C bonds mutually trans are longer (weaker) than those trans to Cr-P bonds ( Table 2). This result reflects the difference in the strength of the metal-to-ligand -bonding 4 Journal of Crystallography [21]. The aromatic rings in 1 as expected have usual bond lengths and angles.

Conclusion
In conclusion, we have shown the synthesis and molecular structure of cis-chelated tetracarbonylchromium(0) complex 1. The Cr-atom has a distorted octahedral arrangement with four CO ligands and two P-centers. The two Cr-C bonds mutually trans are longer (weaker) than those trans to Cr-P bonds due to the various strengths of the metal-to-ligand -bonding.