Porphyrins, mass spectra

Fig. 7. Mass spectrum of porphyrin-like pigment, made from CO, Dj, and ND3 by a Fischer-Tropsch-type synthesis (Hayatsu et al., 1972). It resembles porphyrins in optk and chemical characteristics, but lacks the expected peak at mass 290 from the doubly-charged molecular ion...

We thank Unilever Research and the University of York for financial assistance and the EPSRC Mass Spectrometry Service, Unversity of Wales, Swansea for measuring the electrospray mass spectrum of iron(III) tetra(2,6-dichloro-3-sulfonatophenyl)porphyrin. 

The identification of petroporphyrins rests heavily on UV-visible and mass spectroscopy. In the former, the region of the UV-visible spectrum that gives the most information are the Q bands, between 480-700 nm. As was explained in Chapter 3, the Q band structure is a powerful indicator of the substitution pattern around the porphyrin macrocyclic nucleus. The pattern of Q band intensities that goes IV>I>II>III, is indicative of a phyllo-type substitution pattern, typically displayed by DPEP. As a vanadyl complex, the Q band structure collapses to two bands. So, once a pure sample of VODPEP has been obtained, mass spectroscopy gives an accurate molecular mass. Acid work-up, followed by neutralisation, generates a metal-free porphyrin, whose UV-visible spectrum shows the typical DPEP Q band structure, while the mass spectrum confirms the loss of the V=0 unit. 

Sanders (14) has exploited the strong and selective coordination of phosphine donor groups to Ru(II) to construct hetero-dimetallic porphyrin dimers (17, Fig. 5). An alkyne-phosphine moiety introduced on the periphery of a free base or metalloporphyrin (M = Zn or Ni) spontaneously coordinates to a Ru(II)(CO) porphyrin when the two porphyrins are mixed in a 1 1 ratio. Coordination is characterized by a downfield shift of the 31P resonance (A<531P = 19 ppm). There is no evidence of self-coordination of the zinc porphyrin at 10 6 m in toluene, there is no shift in the Soret band in the UV-Vis absorption spectrum. The Ni-Ru dimer was observed by MALDI-TOF mass spectrometry. Heating the Ru(II)CO porphyrin with 2 equivalents of the phosphine porphyrins led to quantitative formation of trimeric assemblies. 

There are 1H NMR, electrochemical,890 electronic232,895 as well as mass spectral data82 on many of these complexes. A rich resonance Raman spectrum of Os(OEP)py2 has been measured many of the porphyrin ligand fundamentals are resonance-enhanced.896... 

A 5 mg (0.0068 mmol) porphyrin (8a) was dissolved in 0.5 mL 1,2-dichlorbenzene, then 4.5 mL DMF, 7 mg (0.015 mmol) ytterbinm acetylacetonate (3) and 5 mg lithium chloride were added. The mix was maintained for 15 min at 145°C and power 650 w in microwave oven. When reaction mass was cooled solvents were deleted at lowered pressure, and porphyrin complex was isolated by preparative chromatography on silica gel plates in chloroform. Weight 4 mg (58.4%). UV-vis 417.6 553.4 590.4 mn. Luminescent spectrum, 1. 980 nm (DMSO). 

Example The FD spectrum of a ruthenium-carbonyl-porphyrin complex shows an isotopic pattern very close to the theoretical distribution (Chap. 3.2.8). The loss of the carbonyl ligand chiefly results from thermal decomposition. A spectrum accumulated close to BAT (scans 19-25, EHC 25-30 mA) is nearly devoid of CO loss, while a spectrum accumulated of scans 30-36 (35-40 mA) shows significant CO loss (Fig. 8.20). This is demonstrated by comparison of the total ion chromatogram (TIC) with the reconstructed ion chromatogram (RIC) of IVE and [M-CO]" (Chap. 5.4). The FD spectrum of a lower-mass complex was essentially devoid of signals of CO loss because lower emitter currents were sufficient to effect desorption [117]. 

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