intensity, are identical with those observed for the complex [((C5Me5)(CO),Fe}P(Cr(CO)5]=PAryl][9~ and the complex [((C5Mes)C0)2Fe)As(Cr(C0)5)=PAryl],~'"1 thus indicating a similar o-donor/n-acceptor relationship of the ligands [((C5Me5)(CO)ZFe}E'=E2Aryl] (El, E2 = P, As) toward the Cr(CO)s group. In the mass spectra (EI) of 4 and 5 , the peaks with the largest m / z value correspond to the molecular ions, whereas the molecular ion peak of 6 was not observed under comparable conditions. In the FD mass spectrum of 6, the molecular ion of 3 produces the peak of greatest intensity. An additional signal at m/z=918 (37%) is assigned to 5 . The facile fragmentation of 6 to 3 and 5 is possibly due to the very bulky substituents. As-PI 2.316(1), As-P2 2.350(2), P b P 2 2.207(2), As-C 2.010(6), Fel-PI 2.373(2), Fe2-P2 2.326(2); PI-As-P2 56.5(1), As-PI-P2 62.5(1), As-P2-PI 61.0(1), PI-As-C 105.8(1), P2-As-C 104.5(2), As-PI-Fel 110.5(1), P2-PI-Fel 1 l7.l(l), As-P2-Fe2 124.6(1), PIbP2-Fe2 105.3(1).The X-ray structure analysis of 4 is of particular importance['" since there is little available structural information on molecules containing As-P and such data are fully lacking for As-P three-membered rings. The basic framework of the molecule consists of an ASP, triangle in which the As-P2 bond (2.350(2) A), with the substituents in cis orientation, is slightly lengthened compared with the As-PI bond (2.316(1) A). The P-P bond lengths (2.207(2) A) correspond to the normal As expected, the endocyclic angle at the As atom (56.5(1)") is smaller than those at the phosphorus centers (61.0(1)' and 62.5(1)').The [(~5-CsMes)(CO),Fe] groups on P1 and P2 are oriented in a trans fashion. The steric bulk of the substituents on the ASP, framework results in markedly increased exocyclic bond angles at P1 (110.5", 117.1 ") and P2 (1 24.6 O , 105.3 ").
Experimental procedureNMR spectra recorded in COD6 at 22°C; 'H NMR, 200 MHz; IR spectra recorded in cyclopentane. 2: A 2.5 M solution of n-butyllithium in hexane (23 mL) was added dropwise to a solution of I-bromo-2,4,6-tri-tert-butylhenzene (18.1 g, 55.6 mmol) in T H F (250mL). After stirring for 1 h at -5O"C, the reaction mixture was cooled to -70°C and treated dropwise with AsCI, (4.7 mL, 55.6 mmol). The green reaction solution was evaporated to dryness (-30°C) and the residue was dissolved in n-pentane (150 mL), the resulting solution filtered, and the filtrate concentrated until the onset of crystallization. Colorless crystalline needles formed at -28°C and were recrystallized from n-pentane. Yield
4-6:A solution of 1 (1.40 g, 3.30 mmol) [7] in T H F (30 mL) at 0°C was treated with 2 (1.29 g, 3.30 mmol), resulting in a spontaneous change in color from red-brown to dark green. The reaction mixture was stirred for an additional 5 min at 20°C and then evaporated to dryness. The solution of the 5.3g (24%) 2. ' H NMR: 6= 1-15 (s, 9H,p-6Bu), 1.51 (s, ISH, o-IBu), 7.44 residue in 20 m L of ether afforded red-violet crystals of 4 at -28°C (0.14 g, lO%). 'H NMR: 6= 1.39 (s, 9H,p-tBu), 1.53 (s, 15H...
