Dendritic metalloporphyrins with a distal H-bond donor as mimics of haemoglobinElectronic supplementary information (ESI) available: procedures for the synthesis of 1 and 5 and iron(ii) insertion into the dendritic porphyrins including full spectral characterisation and complete EPR characterisation of the complex 22·Co(dmim) and the corresponding oxygenated complex. See http://www.rsc.org/suppdata/ob/b2/b212468h/