J . A m . Chem. SOC.1983, 105, 3014-3022
3014
adenosine moiety compared with that of the adenosine residue of the modified base residue, so that conclusions reached with is expected to be overruled to some extent by the even greater t-adenosine derivatives should be transferred to the unaltered affinities of the di- and triphosphate groups. nucleotide system with reservations. Predictions for mixed ligand complexes (section 5) are more Acknowledgment. We thank K. Aegerter of the Institute for difficult, as certain groups may be released from the coordination Organic Chemistry for recording the 90-MHz N M R spectra and sphere of a metal ion due to the participation of a n additional R. Baumbusch for the skillful performance of the potentiometric ligand. This could often mean that ternary complexes with tp H titrations, which were evaluated on a computer Univac adenine nucleotides are of relatively low stability compared with 1100/81 made available by the Rechenzentrum der Universitat their binary parent complexes (eq 7 and 8). However, in cases Basel. This support, a research grant from the Swiss National where an intramolecular ligand-ligand interaction is p o ~ s i b l e ~ ~ - ~ ~ , * ~ Science Foundation, and grants toward the costs of the t-adenine between aromatic-ring systems, or a hydrophobic interaction with derivatives from the CIBA-Stiftung Basel and the Stiftung der an alkyl residue, the e-adenine moiety is expected to be about as Portlandcementfabrik Laufen are also gratefully acknowledged. effective as the adenine group itself. Overall one may conclude that in systems which involve metal Registry No. Mg, 7439-95-4; Mn, 7439-96-5; Co, 7440-48-4; Ni, ions and t-adenine nucleotides, the structural arrangements will 7440-02-0; Cu, 7440-50-8; Zn, 7440-66-6; Cd, 7440-43-9; 1,@-etheneoften be altered, mainly due to the increased metal ion affinity adenosine, 39007-51-7; t-adenosine L-tryptophan adduct, 85048-85-7.
Preparation and Properties of Dinitrogen Trimethylphosphine Complexes of Molybdenum and Tungsten. 4. Synthesis, Chemical Properties, and X-ray Structure of cis-[M o ( N ~ ) ~ ( P M ~The ~ ) ~Crystal ]. and Molecular Structures of trans-[ Mo( C2H4)2(PMe3),] and
trans,mer-[M~(C~H~)~(CO)(PMe~)~] Ernest0 Carmona,*+Jose M. Marin,+Manuel L. Poveda,+Jerry L. Atwood,** and Robin D. Rogers*s Contribution f r o m the Departamento de Quimica Inorgrinica, Facultad de Quimica, Universidad de Seuilla, Sevilla. Spain, the Department of Chemistry, University of Alabama, University, Alabama 35486, and the Department of Chemistry, Northern Illinois University, Dekalb, Illinois 601 15. Received October 4, 1982
Abstract: The complex cis- [Mo(N,),(PMe,),] (1) has been prepared by reduction of [MoCI,(PMe,),] with dispersed sodium under dinitrogen. Loss of ligating dinitrogen in 1 readily occurs by oxidation with alkyl halides, RX (X = CI, R = Me3SiCH2; X = Br, R = Et; X = I, R = Me), to yield the monomeric Mo(I1) halo derivatives trans-[MoX2(PMe3),] (X = CI, Br, and I) or by substitution with (i) carbon monoxide to give [Mo(CO),(PMe,),) complexes ( x = 2,3), (ii) trimethylphosphine under argon to afford [Mo(N2)(PMeJ5] (2), or (iii) ethylene to yield t r a n s - [ M ~ ( C ~ H , ) ~ ( P M e(3). ~ ) , ]One of the phosphine ligands (4). The structures of complexes 1,3, and in 3 can be easily exchanged by C O to form trans,mer-[M~(C~H~)~(CO)(PMe~)~] 4 have been determined by X-ray crystallography. 1 crystallizes in the monoclinic space group P2,/c with unit cell parameters a = 9.371 (4) A, b = 15.890 (6) A, c = 16.692 (7) A, p = 106.58 (4)O, and D,= 1.27 g cm-3 for Z = 4. Least-squares refinement based on 1720 independent observed reflections led to a final R value of 0.038. Complex 3 belongs to the monoclinic space group P2,/n with a = 10.165 (3) A, b = 13.683 (3) A, c = 17.139 (4) A, p = 98.84 (3)'. and D, = 1.29 g cm-) for Z = 4. The final R value based on 2715 observed reflections was 0.043. 4 is also monoclinic, crystallizing in the space group P2,/n with a = 10.637 (3) A, b = 13.069 (3) A, c = 15.201 (4) A, p = 98.45 (2)O, and D, = 1.30 g cm-3 for Z = 4. It was refined to a final R value of 0.037 on the basis of 2764 independent observed reflections. In 1 the cis N ligands are coordinated to the molybdenum atom at a Mo-N bond distance of 1.97 (1) A. In 3 and 4 the planes formed by the two carbons of each of the trans ethylene ligands and the Mo atom are perpendicular and eclipse the trans P-Mc-P bonds. The average M&(ethylene) distance is 2.270 (5) A in 3 and 2.29 ( 3 ) A in 4.
Molecular dinitrogen complexes of molybdenum have received considerable attention in the past few years in the hope of finding model systems for the binding of N 2 and subsequent transformation into ammonia and amines.II2 The complexes studied generally contain tertiary phosphine as coligands, particular attention having been devoted to trans- [Mo(N,),(dppe),] (dppe = 1,2-bis(diphenyIphosphine)ethane). Although up to four groups of dinitrogen complexes of molybdenum can be e n v i ~ a g e d for ,~ Universidad de Sevilla. University of Alabama. 8 Northern Illinois University f
0002-7863/83/1505-3014$01.50/0
zerovalent molybdenum they are basically of two types,, [M(N2)2P4]and [M(arene)P2],N2 (n = 1,2) (P = phosphorus donor, either mono- or bidentate phosphine). The range of complexes (1) Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. Reu. 1978, 78, 5 89-625. (2) 'New Trends in the Chemistry of Nitrogen Fixation"; Chatt, J., da
Camara Pina, L. M., Richards, R. L., Eds.; Academic Press: New York, 1980. (3) Stiefel, E. I . Prog. Inorg. Chem. 1977, 22, 1-223, (4) A complex of composition [MO(CO)~(PC~,),N~] which reversibly loses N2 has been reported recently: Kubas, G. J. J . Chem. SOC.,Chem. Commun. 1980, 61-62.
0 1983 American Chemical Society
J. Am. Chem. SOC.,Vol. 105, No. 10, 1983 3015
Preparation and Properties of M(N2),(PMeJ4 Scheme I PMe3
CMOCI~(THF),I
-
[ MoCI3(PMe3 ) 3 1
(*I, N a d iPs p Mrer3r
[Mo(CO),(PMe3)6-,J
co
/
~is-[Mo(N2)~(PMe~)41
CZH4 9
CMoX2(PMe3141
(X = C1, Br, I)
t r a n s - C M o ( C p H 4 ) 2 (PMe3141
~ ] )also in making workup and hence isolation that can be prepared is however limited, and prior to our ~ o r k , ~ , ~ [ M o ( N ~ ) ( P M ~ , )but of the final product easier. Thus, we have found that the time there were no reports on bis(dinitrogen) complexes of molybdenum the green solution lasts, depends on the active surface of the sodium with monodentate trialkylphosphines as coligands. W e have reused (see Experimental Section). If the phosphine is added too cently shown5 that the reduction of [MoCl,(PMe,),] with sodium soon, the yield of complex 1 diminishes drastically, transamalgam yields a compound of composition [MoCI(N,)(PMe,),], [MoC12(PMe3),] being formed in considerable amounts. All the which behaves as a mixture of trans-[Mo(N2),(PMe3),] and above clearly shows that, as pointed out by Chatt,' the preparation t r ~ n s - [ M o C l ~ ( P M e , ) ~In ] . this paper we report the preparation of dinitrogen complexes of transition metals is still in an essentially of c i s - [ M ~ ( N ~ ) ~ ( P M e(1) , ) ~from l the dispersed sodium reduction empirical state. of [MoCl,(PMe,),], under dinitrogen, and some of its chemical Properties and X-ray Structure of ~ i s - [ M o ( N ~ ) ~ ( P M e(1). ,)~l properties, particularly its smooth and essentially quantitative The pure dinitrogen complex 1 is a yellow crystalline solid, which transformation into [Mo(N,)(PMe,),] (2) and its reaction with becomes opaque or crumbles into a yellow powder when dried in ethylene under mild conditions to afford trans- [Mo(C2H4),vacuo. This has made the preparation of crystals suitable for X-ray (PMe,),] (3). This latter complex binds N 2 to give a species studies difficult. The complex is very soluble in most common formulated as trans,mer-[M~(C~H~)~(N~)(PMe~),] (which in turn organic solvents; crystallization from petroleum can only be can be converted into 3 by interaction with PMe,) and reacts with achieved at -78 "C or at -20 "C with very concentrated solutions. C O to yield trans,mer-[M~(C,H,)~CO(PMe~)~] (4). These and other reactions summarized in Scheme I are discussed together It is very air sensitive, both in solution and in the solid state, decomposing immediately upon exposure to air. Complex 1 is with the X-ray structures of complexes 1, 3, and 4. Part of this only moderately thermally stable. Although it can be stored work has been briefly communicatede6 When this work was indefinitely at 0 "C, both as a solid or in petroleum ether solutions, essentially finished, a preliminary communication dealing with it decomposes rapidly a t 40-50 "C. Thermal decomposition is 2 and 3 appeared.' probably initiated by loss of one of the dinitrogen ligands to yield Results and Discussion a 5-coordinate intermediate species [Mo(N,)(PMe,),]. This is Synthesis of cis-[Mo(N,),(PMe,),] (1). The new dinitrogen in accord with the easy substitution of one of the dinitrogen complex was first prepared, in ca. 30-40% yield by the two-step molecules in 1 by PMe, to give [ M O ( N , ) ( P M ~ ~(2) ) ~ ]and by other sequence of eq 1. The addition of a tetrahydrofuran solution of neutral ligands (see below). It is also noteworthy in this respect, that while petroleum ether solution of 1 decompose rapidly upon heating a t 40-50 "C, no decomposition is apparently observed at 50-60 "C, for several hours, under 50 psi of N2. The dissociative CiS-[MO(N2)2(PMe3)41 (1) activation of one of the M w N 2 ligands has been shown to be the rate-controlling step in a number of reactions of bis(dinitrogen) freshly prepared [MoCI3(PMe3),] to a vigorously stirred suspension complexes of of finely divided sodium metal in tetrahydrofuran produces a IR and N M R spectroscopic data for 1 are in accord with the change in color from yellow to deep green. The green color persists for relatively long periods of time (30-45 min), then darkens, and proposed formulation as a cis bis(dinitrogen) complex. The IR spectrum shows two strong absorptions at 2010 and 1965 cm-t finally turns dark yellow-brown. The formation of a green solution (hexane), as expected for the two N N stretching modes (Al,Bl) is also observed in the early stages of the preparations5 of in the C, symmetry characteristic of the Mo(NJ2P, coordination [MCl(N2)(PMe3)4]( M = Mo, W), but attempts to isolate this sphere of this complex. The cis distribution of the dinitrogen intermediate species have been unsuccessful. The choice of the ligands leaves the four remaining coordination sites of an octaprecursor is of the greatest importance; as found in other related hedral configuration to the four trimethylphosphine ligands, and system^,',^ no dinitrogen species being formed from the reduction this situation is easily recognized both in the ' H and in the 31P(1H1 of either [MoCl,(THF),] or [MoCI3(PMe3),] in the presence of N M R spectrum. Thus, the proton N M R spectrum shows two an excess of phosphine or from [MoC12(PMe3),]. The yield of reaction 1 can be substantially improved (50-60%) by addition sets of signals of equal intensity, each consisting of three lines with the central ones a t 6 1.4 and 1.2, while the 31PN M R spectrum of ca. 80% of the required amount of phosphine approximately shows two slightly distorted triplets that can be approximately 20 min after the appearance of the green color. On the other hand, the nature of the reducing agent used is also of importance not -4.85, dpx -6.90, interpreted in terms of an A2X2system with and ,J(PAPX) = 18 Hz. This compares well with data reported9 only in determining the composition of the reduced dinitrogen for cis- [Cr(N2)2(PMe3)4]. complex (as indicated earlier, the use of sodium amalgam proThe molecular structure and atom labeling scheme for cisduces5 [MoCI(N2)(PMe3),] and only small amounts of cis[Mo(N2),(PMeJ4] (1) are presented in Figure 1. The relative thermal instability of complex 1 is apparently reflected in the high (5) Carmona, E.; Marin, J. M.; Poveda, M. L.; Atwood, J. L.; Rogers, R. thermal motion of the atoms. The only resolvable disorder, D. Polyhedron 1983, 2, 185-193. however, involved the rotational disorder of the carbons bonded (6) (a) Carmona, E.; Marin, J. M.; Poveda, M. L.; Atwood, J, L.; Rogers, ~~~~
R. D.; Wilkinson, G . Angew. Chem., In?.Ed. Engl. 1981,21,441-442; Angew Chem. Suppl. 1982, 11 16-1 120. (b) Carmona, E.; Marin, J. M.; Poveda, M. L.; Rogers, R. D.; Atwood, J. L. J . Organomet. Chem. 1982,238, C63-C66. (7) Cloke, F. G. N.; Cox, K. P.; Green, M. L. H.; Bashkin, J.; Prout, K. J . Chem. Sac., Chem. Commun. 1982, 393-394.
(8) Carter, B. J.; Bercaw, J. E.; Gray, H. B. J . Organomet. Chem. 1979, 181, 105-116. (9) Karsch, H. H. Angew. Chem., In?. Ed. Engl. 1977, Id, 56-51.
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Carmona et al.
J . Am. Chem. Soc., Vol. 105, No. 10, 1983 Table I. Bond Distances (A) and AnFles (deg) for cis- [Mo(N,), (PMe,), 1 (1) Distances 2.441 (3) Mo-P(2) Mo-P(l) 2.449 (3) Mo-P(4) Mo-P(3) Mo-N(3) 1.97 (1) Mo-Ii(1) 1.84 (1) p(1)-c(2) P( 1)-C(1) 1.87 (2) P(2)-C(4) p( 1)-c(3) 1.83 (3) P(2)-C(6) P(2)-C(5) 1.87 (2) p(2)-c(5) P(2)-C(4) 1.80 (3) p(3)-c(7) P(2)-C(6) 1.89 (2) p(3)-c(9) P(3)-C(8) 1.84 (3) P(4)-C(ll) P(4)-C(10) 1.81 (2) N(l)-N(2) P(4)-C(12) N(3)-N(4) 1.14 (1)
2.459 (3) 2.456 (3) 1.97 (1) 1.85 (2) 1.87 (2) 1.81 (2) 1.81 (3) 1.85 (1) 1.84 (2) 1.85 (2) 1.15 (1)
Angles 92.9 (1) 93.9 (1) P(l)-Mo-P(3) P(l )-Mo-P(2) 93.0 (1) 95.3 (1) P(l)-Mo-P(4) P(2)-Mo-P(3) 168.3 (1) 94.4 (1) P(3)-Mo-P(4) P(2)-Mo-P(4) 87.2 (4) 178.4 (4) P(2)-Mo-N(1) P(l)-Mo-N(l) 88.2 (3) 85.8 (4) P(4)-Mo-N(1) P(3)-Mo-N(1) Figure 1. Molecular structure of cis-[Mo(N,),(PMeJ,] (1) with the 91.9 (3) P(2)-Mo-N(3) 174.2 (3) P(l)-Mo-N(3) atoms represented by their 50% probability ellipsoids for thermal motion. 84.6 (3) P(4)-Mo-N(3) 85.1 (3) P(3)-Mo-N(3) The disorder of atoms C(4)-C(6) is not shown. 121.7 (5) 87.0 (5) Mo-P(l)-C(l) N(l)-Mo-N(3) 121.9 (6) C(l)-P(l)-C(2) 99.0 (8) Mo-P( 1)-C(2) to P(2) (see Experimental Section). As a result of the high thermal 113.9 (6) C(l)-P(l)-C(3) 98.4 (8) MO-P( 1)-C(3) motion the standard deviations associated with most of the bond 98.8 (9) Mo-P(2)-C(4) 120.1 (8) C(2)-P( 1)-C(3) distances and angles are somewhat high as can be seen in Table 121.4 (9) C(4)-P(2)-C(5) 94 (1) Mo-P(2)-C(5) I. Comparison with other structures should bear this in mind. 101 (1) 115.4 (9) C(4)-P(2)-C(6) MO-P(2)-C(6) Mo-P(2)-C(4) 119 (1) 101 (1) C(5)-P(2)-C(6) ~ i s - [ M o ( N , ) , ( P M e ~ ) ~(1) 1 is essentially octahedral. The four 122 (1) C(4)-P(2)-C(5) Mo-P(2)-C(5) 89 (2) phosphine ligands are coordinated to the molybdenum atom at 114 (1) C(4)-P(2)-C(6) 97 ( 2 ) Mo -P (2)-C(6) an average Mo-P separation of 2.451 (8) A. There is no sigMo-P(3)
